View source for Number sign

{{About|the {{char|#}} symbol|the abbreviations ''№''  and ''No.'' |Numero sign|a number's mathematical sign|Sign (mathematics)}}
{{Short description|Typographic symbol (#)}}
{{Infobox symbol
|mark=&num;
|unicode = {{unichar|0023|html=}}
|see also = {{unichar|2116|nlink=}}<br />{{unichar|2114}}
}}
The symbol {{char|'''#'''}} is known as the '''number sign''',<ref name="oedNumberSign">{{cite web |url=https://en.oxforddictionaries.com/definition/number_sign |archive-url=https://web.archive.org/web/20180403112505/https://en.oxforddictionaries.com/definition/number_sign |url-status=dead |archive-date=April 3, 2018 |title=number sign |website=Oxford English Dictionary}}</ref> '''hash''',<ref name="oedHash">{{cite web |url=https://en.oxforddictionaries.com/definition/hash |archive-url=https://web.archive.org/web/20171231152808/https://en.oxforddictionaries.com/definition/hash |url-status=dead |archive-date=December 31, 2017 |title=hash |website=Oxford English Dictionary}}</ref> and the '''pound sign'''<ref>{{cite web |url=https://en.oxforddictionaries.com/definition/pound_sign |archive-url=https://web.archive.org/web/20180403051651/https://en.oxforddictionaries.com/definition/pound_sign |url-status=dead |archive-date=April 3, 2018 |title=pound sign |website=Oxford English Dictionary |access-date=5 May 2016}}</ref> and has a variety of other names. The symbol has historically been used for a wide range of purposes including the designation of an [[ordinal number]] and as a [[Typographic ligature|ligatured]] abbreviation for [[Pound (mass)|pounds avoirdupois]] – having been derived from the now-rare {{char|℔}}.<ref name="Houston">{{cite book |last1=Houston|first1=Keith |title=Shady Characters: The Secret Life of Punctuation, Symbols, and Other Typographical Marks |publisher=W. W. Norton & Company |year=2013 |isbn=978-0-393-06442-1 |chapter-url=https://books.google.com/books?id=3fbWAAAAQBAJ&pg=PA41 |pages=41–57 |chapter=The Octothorpe }}</ref>

Since 2007, widespread usage of the symbol to introduce [[metadata tag]]s on [[social media]] platforms has led to such tags being known as '[[hashtag]]s',<ref>{{cite book|last=Piercy |first=Joseph |title=Symbols: A Universal Language|chapter-url=https://books.google.com/books?id=XRbdAgAAQBAJ&pg=PT84 |chapter=Part III: Symbnols of value, ownership and exchange |access-date=4 October 2014 |date=25 October 2013 |publisher=Michael OMara|isbn=978-1-78243-073-5 |pages=84–85}}</ref> and from that, the symbol itself is sometimes called a '''hashtag'''.<ref name=hashtag>{{cite web |url=https://www.britannica.com/dictionary/eb/qa/why-is-the-symbol-called-the-hashtag-in-twitter |title=Why is the symbol # called the hashtag in Twitter? |website=The Britannica Dictionary |access-date=2022-09-23 |archive-date=2022-09-23 |archive-url=https://web.archive.org/web/20220923225746/https://www.britannica.com/dictionary/eb/qa/why-is-the-symbol-called-the-hashtag-in-twitter |url-status=live }}</ref>

The symbol is distinguished from similar symbols by its combination of level horizontal strokes and right-tilting vertical strokes.

==History==
[[File:Pfund.svg|thumb|A stylized version of the abbreviation for {{lang|la|[[Roman pound|libra pondo]]}} ({{translation|pound weight}})|upright]]
[[File:Libra pondo abbreviation newton.jpg|thumb|The abbreviation written by [[Isaac Newton]], showing the evolution from {{char|℔}} toward {{char|#}}]]
It is believed that the symbol traces its origins to the symbol {{char|[[wikt:℔|℔]]}},{{efn|{{unichar|2114|nlink=}} }} an abbreviation of the Roman term {{lang|la|[[Roman pound|libra pondo]]}}, which translates as "pound weight".<ref>{{cite book | quote=The Italian ''libbra'' (from the old Latin word ''libra'', 'balance') represented a weight almost exactly equal to the [[avoirdupois]] pound of England. The Italian abbreviation of ''lb'' with a line drawn across the letters was used for both weights. The business clerk’s hurried way of writing the abbreviation appears to have been responsible for the # sign used for 'pound.' | author =Keith Gordon Irwin | title= The romance of writing, from Egyptian hieroglyphics to modern letters, numbers, and signs | page= 125 | location= New York |publisher= Viking Press | year = 1967 | orig-year = 1956 |url=https://archive.org/details/romanceofwriting0000keit/page/125/mode/1up?q=libbra}}</ref><ref name="NewYorker" /> The abbreviation ''lb'' was printed as the dedicated [[Ligature (writing)|ligature]] {{char|℔}}, including a horizontal line across (which indicated abbreviation<ref>{{cite book |title=The Elements of Abbreviation in Medieval Latin Paleography |url=https://archive.org/details/213385262/page/18/mode/2up |pages=18{{ndash}}20 |first=Adriano |last=Cappelli |translator1=David Heimann |translator2=Richard Kay |publisher= [[University of Kansas]] |via=Archive.org}}</ref>).<ref name="NewYorker" /> Ultimately, the symbol was reduced for clarity as an overlay of two horizontal strokes {{char|1==}} across two slash-like strokes {{char|//}}.<ref name="NewYorker">{{cite news|last=Houston|first=Keith|title=The Ancient Roots of Punctuation|url=http://www.newyorker.com/online/blogs/books/2013/09/origins-of-hashtag-manicule-diple-pilcrow-ampersand-explained.html|access-date=16 October 2013|newspaper=The New Yorker|date=2013-09-06|archive-date=2014-06-25|archive-url=https://web.archive.org/web/20140625175614/http://www.newyorker.com/online/blogs/books/2013/09/origins-of-hashtag-manicule-diple-pilcrow-ampersand-explained.html|url-status=live}}</ref> 

In printing, a sign similar to {{char|#}} is used in as a correction symbol in margins to indicate a space is needed between two words, as noted in [[Joseph Moxon]]’s 1683 book ''Mechanik Exercises''<ref>{{Cite book |last=Moxon |first=Joseph |url=https://books.google.com/books?id=BncsAAAAYAAJ&pg=PA262#v=onepage&q&f=false |title=Mechanick Exercises |year=1683 |volume=2 |pages=262}}</ref>, in [[Philip Luckombe]]’s 1770 book on printing<ref>{{Cite book |last=Luckombe |first=Philip |url=https://archive.org/details/bub_gb_MlhAAAAAYAAJ/page/443/mode/1up |title=A concise history of the origin and progress of printing |year=1770 |location=London |pages=443}}</ref> or the 1847 revision of [[Noah Webster]]’s ''Dictionary'' by [[Chauncey A. Goodrich]].<ref>{{Cite book |last=Webster |first=Noah |url=https://archive.org/details/websteramericand00webs/page/1384/mode/1up |title=An American dictionary of the English language |last2=Goodrich |first2=Chauncey A. |year=1847 |pages=1384}}</ref>

A similar sign (like {{char|⌗}}) has also sometimes been used as a sign for the [[ducat]] coin,<ref>{{Cite book |last=von Clausberg |first=Christlieb |title=Demonstrative Rechenkunst |year=1795 |location=Leipzig |pages=[xxxii] |language=de |url=https://www.digitale-sammlungen.de/en/view/bsb10081605?page=38}} The symbol appears near the bottom right of this page of text.</ref><ref>{{Cite book |last=Schiebe |first=August |title=Die Kaufmännische Correspondenz |year=1848 |location=Grimma |pages=39 |language=de |url=https://www.digitale-sammlungen.de/en/view/bsb10291717?page=69}} The symbol appears near the bottom left of this page of text.</ref> other times included with abbreviations starting with D, or as a substitute for the [[milréis]] sign.<ref>{{Cite book |last=Noback |first=Friedrich Eduard |url=https://www.digitale-sammlungen.de/en/view/bsb11358829?page=525 |title=Münz-, Maass- und Gewichtsbuch |publisher=Brockhaus |year=1877 |pages=507 |language=de}}</ref> In some 16th century German accounting manuscripts, the [[numero sign]] ({{not a typo|{{char|№}}}}) is written with an N with two extra lines ornamenting it.<ref>{{Cite book |url=https://www.digitale-sammlungen.de/en/view/bsb00107886?page=8 |title=Rechnung über Einnahmen und Ausgaben für Hans Fugger, Herrn zu Kirchperg und Weissenhorn, vom März 1562, BSB Cgm 5081(1 |date=March 1562 |pages=2v}}</ref>. 
The symbol, printed as {{char|♯}}, is described as the "number" character in an 1853 treatise on [[bookkeeping]],<ref>{{cite book|last1=Crittenden|first1=S. W.|title=An Elementary Treatise on Book-keeping by Single and Double Entry |date=1853 |publisher=E., C., & J. Biddle |location=Philadelphia |page=10 |url=https://archive.org/details/anelementarytre00critgoog/page/n16/mode/1up |access-date=7 February 2023}}</ref> and its double meaning (''number'', ''pound'') is described in a bookkeeping text from 1880.<ref>{{cite book|last1=Duff|first1=C. P.|last2=Duff|first2=W. H.|last3=Duff|first3=R. P.|title=Book-Keeping By Single and Double Entry|date=1880|publisher=Harper and Brothers|page=21|url=https://archive.org/details/bookkeepingbysi00duffgoog/page/n27/mode/1up|access-date= 24 November 2015 |quote=#—Preceding a figure (thus, # 10) means number. <br>#—After a figure (thus, 10 #) means pound.}}</ref> German language references from 1873 or 1892 also shows the symbol for '[[ducat]]' ({{Lang|de|Ducaten}}) or 'number' ({{Lang|de|Nummer}}), printed as {{char|♯}}<ref>{{Cite book |last=Flügel |first=Johann Gottfried |url=https://books.google.com/books?id=sbdJAAAAIAAJ&pg=PT1#v=onepage&f=false |title=Praktische Anleitung zur englischen Handels-Correspondenz |publisher=Friedrich Noback |year=1873 |edition=9 |location=Dresden}}</ref> or {{char|⌗}}, with ''number'' also represented with {{char|⌗º}}.<ref>{{Cite book |last=Rohmeder |first=A. F. |url=https://www.digitale-sammlungen.de/en/view/bsb11611078?page=62,63 |title=Die Abkürzung der Wörter |publisher=Kellerer |year=1892 |location=München |pages=58-59 |language=de}}</ref>{{efn|The {{char|º}} is {{unichar2|º|nlink=}}. Compare with {{unichar2|№|nlink=}} }}

The instruction manual of the [[Blickensderfer typewriter#Model 5|Blickensderfer model 5]] typewriter ({{Circa|1896}}) appears to refer to the symbol as the "number mark".<ref>{{cite book |author= |url=https://site.xavier.edu/polt/typewriters/Blick5manual.pdf#page=16 |title=Method of Operating and Instructions for Practice on the Blickensderfer Typewriter |publisher=K. M. Turner |year=1896 |location=Atlanta, GA |page=14 |quote=It is best to use the 'number mark' for plus; the hyphen for minus, and two hyphens for the sign = |archive-url=https://web.archive.org/web/20211014223637/https://site.xavier.edu/polt/typewriters/Blick5manual.pdf#page=16 |archive-date=Oct 14, 2021}}</ref> Some early-20th-century U.S. sources refer to it as the "number sign".<ref>e.g. J. W. Marley, "The Detection and Illustration of Forgery By Comparison of Handwriting", in {{cite book |url=https://books.google.com/books?id=Z_NEAQAAMAAJ&pg=PA180 |title=Proceedings of the Sixteenth Annual Convention of the Kansas Bankers' Association |publisher=Rusell |year=1903 |location=Kansas City |page=180–181| quote=Recently there were sent by mail to the Kansas banks engraved reproductions of a draft issued by an Ohio bank on its New York correspondent for ten dollars which had been raised to ten thousand dollars and successfully negotiated in Buffalo, New York. It was sent out as a means of advertising a check protecting machine but it will serve us for illustration. I presume many of you, and perhaps all of you, have seen it. The number sign used immediately following the word ten in the body of the draft and part of the line drawn along the unoccupied space from it to the word dollars in the right hand margin had been removed with acid and the word thousand written in. The number sign following the memorandum figures $10 in the end margin had likewise been removed and three ciphers added. The number sign had then been added after both the added word and the added ciphers, so that the draft in its altered form read Ten Thousand#———— Dollars in words in the body and $10000# in figures in the margin with the only significant peculiarity in the make-up of the draft, the number sign following both the written words in the body and the memorandum figures in the margin, relatively in the same position as in the draft as originally issued.}}</ref> A shorthand textbook written in 1903 refers to this symbol as the "pound or number sign" and details its two distinct uses (before and after a number).<ref name="Boyd">{{cite book| title=Boyd's syllabic shorthand text book |edition=second |date=1903 |page=58 |first=Robert |last=Boyd |location=Chicago |publisher= Chicago Correspondence Schools |url=https://archive.org/details/syllabicshorthan00boyd/page/58/mode/1up |quote="Make the (#) pound or number sign thus: 37⁺ = 37 lbs. ⁺37 = No. 37."}}</ref> A 1917 manual distinguishes between two uses of the sign: "number (written before a figure)" and "pounds (written after a figure)".<ref>{{cite book |title=Business Arithmetic for Secondary Schools |first=Ernest L. |last=Thurston |location=New York |publisher=Macmillan |year=1917 |page=419 |url=https://archive.org/details/businessarithme02thurgoog/page/n439/mode/1up|quote=APPENDIX I. SIGNS AND SYMBOLS. [...] #. . . . . . .number (written before a figure). [...] #. . . . . . .pounds (written after a figure). }}</ref> The use of the phrase "pound sign" to refer to this symbol is found from 1932 in U.S. usage.<ref>{{cite book |first=Nancy M. |last=Lawrence |author2=F. Ethel McAfee |author3=Mildred M. Butler |title=Correlated studies in stenography |publisher=Gregg |year=1932 |page=141 |url=https://books.google.com/books?redir_esc=y&id=oCsOAQAAIAAJ&focus=searchwithinvolume&q=Pound+sign |quote= Number or Pound Sign (#) 1. Before figure for ''number''. #16. 2. After figure for ''pound''. }}</ref>

For mechanical devices, the symbol appeared on the keyboard of the [[E. Remington and Sons|Remington]] Standard typewriter ({{Circa|1886}}).<ref>{{cite web|url=http://pds.lib.harvard.edu/pds/view/2574435?n=52&s=4&printThumbnails=no|title=Remington Standard typewriter |location=New York |publisher=Wyckoff, Seamans & Benedict |date=1886 |page=50}}</ref> It appeared in many of the early teleprinter codes and from there was copied to [[ASCII]], which made it available on computers and thus caused many more uses to be found for the character. The symbol was introduced on the bottom right button of [[Push-button telephone|touch-tone]] keypads in 1968, but that button was not extensively used until the advent of large-scale [[voicemail]] (PBX systems, etc.) in the early 1980s.<ref name="Houston" />

One of the uses in computers was to label the following text as having a different interpretation (such as a command or a comment) from the rest of the text. It was adopted for use within internet relay chat ([[Internet Relay Chat|IRC]]) networks circa 1988 to label groups and topics.<ref>"Channel Scope". Section 2.2. {{IETF RFC|2811}}</ref> This usage inspired [[Chris Messina (open source advocate)|Chris Messina]] to propose a similar system to be used on [[Twitter]] to tag topics of interest on the microblogging network;<ref>{{cite web|url=http://www.cmu.edu/homepage/computing/2014/summer/originstory.shtml|title=#OriginStory|publisher=Carnegie Mellon University|date=August 29, 2014|access-date=August 23, 2019|archive-date=June 1, 2019|archive-url=https://web.archive.org/web/20190601233044/https://www.cmu.edu/homepage/computing/2014/summer/originstory.shtml|url-status=live}}</ref><ref>{{cite news |author=Parker, Ashley |date=June 10, 2011 |title=Twitter's Secret Handshake |work=The New York Times |url=https://www.nytimes.com/2011/06/12/fashion/hashtags-a-new-way-for-tweets-cultural-studies.html?_r=1&pagewanted=all |url-status=live |url-access=limited |access-date=July 26, 2011 |archive-url=https://web.archive.org/web/20110617001914/https://www.nytimes.com/2011/06/12/fashion/hashtags-a-new-way-for-tweets-cultural-studies.html?_r=1&pagewanted=all |archive-date=Jun 17, 2011}}</ref> this became known as a [[hashtag]]. Although used initially and most popularly on Twitter, hashtag use has extended to other social media sites.<ref>{{cite news |last=Warren |first=Christina |title=Facebook finally gets #hashtags |website=CNN |url=http://www.cnn.com/2013/06/12/tech/social-media/facebook-hashtags/index.html |url-status=live |access-date=July 16, 2006 |archive-url=https://web.archive.org/web/20130613102217/https://www.cnn.com/2013/06/12/tech/social-media/facebook-hashtags/index.html |archive-date=Jun 13, 2013}}</ref>
{{anchor|Other_names_in_English}}

==Names==

===Number sign===
''Number sign'' is the name chosen by the [[Unicode Consortium]]. Most common in Canada<ref>{{cite book |editor-last=Barber |editor-first=Katherine |title=The Canadian Oxford dictionary |date=2004 |publisher=Oxford University Press |location=Toronto |isbn=0195418166 |edition=2nd}}</ref> and the northeastern United States.{{citation needed|date=October 2020}}<!-- I am from Massachusetts and it certainly was called "number sign" there-->  American telephone equipment companies which serve Canadian callers often have an option in their programming to denote [[Canadian English]], which in turn instructs the system to say "number sign" to callers instead of "pound".<ref>{{cite web |title=Norstar Voice Mail 4.1 {{!}} Software Add-on Guide |publisher=[[Nortel]] |page=12 |url=https://downloads.avaya.com/css/P8/documents/100141949 |access-date=2015-12-11 |archive-date=2015-12-22 |archive-url=https://web.archive.org/web/20151222090552/https://downloads.avaya.com/css/P8/documents/100141949 |url-status=live }}</ref> This name is not used in many locations outside North America: in other countries that use Latin script, the term "number sign" may mean symbols like [[numero sign|''No.'']].

===Pound sign===
In the United States and Canada, the {{keypress|#}} key on a phone is commonly referred to as the ''pound sign'', ''pound key'', or simply ''pound''. Dialing instructions to an extension such as {{keypress|#77|chain=}}, for example, can be read as "pound seven seven".<ref name="nyt">{{cite news | url=https://www.nytimes.com/1991/03/24/magazine/on-language-hit-the-pound-sign.html | title=On Language; Hit the Pound Sign | author=William Safire | newspaper=[[The New York Times]] | access-date=May 21, 2011 | date=March 24, 1991 | author-link=William Safire | archive-date=July 21, 2010 | archive-url=https://web.archive.org/web/20100721065416/http://www.nytimes.com/1991/03/24/magazine/on-language-hit-the-pound-sign.html | url-status=live }}</ref> This name is rarely used elsewhere, as the term ''pound sign'' is understood to mean [[pound sign|the currency symbol £]].

===Hash===

In the United Kingdom and Australia,<ref>{{cite news |url=https://www.theguardian.com/artanddesign/2010/dec/08/hash-symbol-twitter-typography |title=How the # became the sign of our times |newspaper=[[The Guardian]] |access-date=30 December 2014 |archive-date=31 December 2014 |archive-url=https://web.archive.org/web/20141231061916/http://www.theguardian.com/artanddesign/2010/dec/08/hash-symbol-twitter-typography |url-status=live }}</ref><ref>{{cite web |url=https://getproofed.com.au/writing-tips/writing-tips-how-to-use-the-hash-sign/ |title=Writing Tips: How to Use the Hash Sign (#) |website=GetProofed |date=6 February 2020 |quote=In Australia, however, it was better known as the 'hash' sign and only used to mean 'number'. |access-date=9 January 2023 |archive-date=9 January 2023 |archive-url=https://web.archive.org/web/20230109105954/https://getproofed.com.au/writing-tips/writing-tips-how-to-use-the-hash-sign/ |url-status=live }}</ref> it is frequently called a ''hash'' (probably from ''hatch'', referring to cross-[[hatching]]<ref>{{cite dictionary |url=http://www.oed.com/view/Entry/84445 |title=Hash sign |dictionary=Oxford English Dictionary |access-date=14 October 2013 |archive-date=16 November 2018 |archive-url=https://web.archive.org/web/20181116124751/http://www.oed.com/view/Entry/84445 |url-status=live }}</ref>). This is also called a {{wikt-lang|en|hash mark}} or {{wikt-lang|en|hashmark}}.<ref>{{Cite web |title=HASH MARK Definition & Meaning |work=Dictionary.com |url=https://www.dictionary.com/browse/hash-mark |access-date=2025-12-26}}</ref>

The term ''hash sign'' is found in South African writings from the late 1960s.<ref>''Research Review. Navorsingsoorsig'' vols. 18–21, pp. 117, 259 (1968)</ref>

Programmers also use this term; for instance {{code|#!}} is "hash, bang" or [[Shebang (Unix)|"shebang"]].<ref>{{Cite book |last=Dearle |first=Fergal |url=https://www.google.com/books/edition/Groovy_for_Domain_specific_Languages/RNtOCwAAQBAJ?hl=en&gbpv=1&dq=%2522shebang%2522+%2522%2523!%2522&pg=PA27&printsec=frontcover |title=Groovy for Domain-specific Languages |date=September 28, 2015 |publisher=[[Packt Publishing]] Ltd |isbn=978-1-84969-541-1 |pages=27|language=en}}</ref>

===Hashtag===

Derived from the previous, the word ''[[hashtag]]'' is often used when reading social media messages aloud, indicating the start of a hashtag. For instance, the text {{code|#foo}} is often read out loud as "hashtag foo" (as opposed to "hash foo"). This leads to the common belief that the symbol itself is called ''hashtag''.<ref name=hashtag /> [[Twitter]] documentation referred to it as "the hashtag symbol".<ref>{{cite web|url=https://support.twitter.com/articles/49309|title=Using hashtags on Twitter|website=Twitter|access-date=5 May 2016|archive-date=4 May 2016|archive-url=https://web.archive.org/web/20160504192917/https://support.twitter.com/articles/49309|url-status=live}}</ref>

===Hex===

The term ''hex'' is commonly used in Singapore and Malaysia, as spoken by many recorded telephone directory-assistance menus: "Please enter your phone number followed by the 'hex' key". The term ''hex'' is formally discouraged in Singapore in favour of ''hash''.{{cn|date=February 2025}} In Singapore, the symbol is also called "hex" in apartment addresses, where it precedes the floor number.<ref>{{cite web|title=A Dictionary of Singlish and Singapore English|author=Jack Tsen-Ta Lee|url=http://mysmu.edu/faculty/jacklee/singlish_H.htm#hex|access-date=14 January 2016|archive-date=19 January 2016|archive-url=https://web.archive.org/web/20160119143130/http://www.mysmu.edu/faculty/jacklee/singlish_H.htm#hex|url-status=live}}</ref><ref>{{cite web|title=Address Formats|url=http://www.informatica.com/products/data-quality/data-as-a-service/address-verification/address-formats.html?code=SGP|access-date=14 January 2016|archive-date=8 March 2016|archive-url=https://web.archive.org/web/20160308064622/https://www.informatica.com/products/data-quality/data-as-a-service/address-verification/address-formats.html?code=SGP|url-status=live}}</ref>

=== <span class="anchor" id="Octothorpe"></span><span class="anchor" id="Octathorp"></span><span class="anchor" id="Octatherp"></span>Octothorp ===
{{wikt|octothorp|octothorpe}}
The word '''octothorp'''{{efn|known by various spellings, such as '''octothorpe''' and {{Citation needed span|'''octathorp'''|date=March 2026}}}} or '''octatherp''' was invented by workers at the [[Bell Telephone Laboratories]] by 1968,<ref>{{cite magazine |url=http://www.svpal.org/~dickel/octothorp/Encore_magazine.pdf |magazine=Encore |title=Pressing Matters: Touch-tone phones spark debate |author=Hochhester, Sheldon |date=2006-09-29 |access-date=2006-12-17 |archive-date=2007-09-26 |archive-url=https://web.archive.org/web/20070926100216/http://www.svpal.org/~dickel/octothorp/Encore_magazine.pdf |url-status=live }}</ref> who wanted to add an eleventh and a twelfth key to the [[telephone keypad]] and needed named symbols to identify them.<ref>"You Asked Us: About the * and # on the New Phones", ''The Calgary Herald'', September 9, 1972, page 90.</ref> While there is typically agreement that ''[[octo-]]'' or ''[[octa-]]'' is here the common prefix meaning [[eight]], various stories abound about the nature of the ''thorp''. Don MacPherson is said to have created the word by combining ''octo'' and the last name of [[Jim Thorpe]], an Olympic medalist.<ref>Ralph Carlsen, "What the ####?" ''Telecoms Heritage Journal'' 28 (1996): 52–53.</ref><!-- TODO: Jim Thorpe had eight children. But is that mentioned in this or any source? I can't find the text of Carlsen. The Merriam-Webster New Book of Word Histories, 1991, vaguely alludes to "a man named Thorpe who had eight children". https://www.irregardlessmagazine.com/articles/how-to-pronounce-octothorpe/ seems to be working from the same source when it mentions "There’s a story about a great man named Thorpe who had eight children.", although it then also immediately mentions Jim Thorpe (who is not mentioned in The Merriam-Webster New Book of Word Histories) as a different possible alternative. I think this is all barking up the wrong tree anyway, as Kerr's account is more credible, but it would be an interesting connection. --> Lauren Asplund declared that he and Howard Eby invented the word in 1964:<ref>      Kerr, Douglas A. “{Personal Correspondence}”. Keith Houston, May 1, 2011. Cited in: {{cite web |title=The Octothorpe, part 2 of 2 – Shady Characters |url=https://shadycharacters.co.uk/2011/05/the-octothorpe-part-2-of-2/ |date=22 May 2011}} This Shady Characters article conflates this story with the "difficult to pronounce" story from Kerr's 2006 essay.</ref>
{{quote|We finally decided in a jocular way to call the pound sign an “Octotherp”. That was because it had eight points and “therp” sounded Greek and also seemed to go well with the “octo” portion of the word.}}

Doug Kerr<!-- not [[Doug Kerr]], the Canadian football coach --> has written two essays about his recollections on the subject. In the first, in 2006, he wrote:<ref name="Kerr">{{cite web |url=http://dougkerr.net/pumpkin/articles/Octatherp.pdf |author=Douglas A. Kerr |title=The ASCII Character "Octatherp" |date=2006-05-07 |access-date=2010-08-23 |archive-date=2010-12-15 |archive-url=https://web.archive.org/web/20101215025150/http://dougkerr.net/pumpkin/articles/Octatherp.pdf |url-status=live }}</ref>
{{quote|John C. Schaak and Herbert T. Uthlaut, engineers from two of the Bell Telephone companies [...] had read with interest the part of my report in which I regretted the absence of a unique typographical name for the character "#", and said they had solved my problem by coining one, ''octatherp''. They said that it had no etymological basis, but they had been guided by one principle. They said they were irritated that I had rejected some candidate characters they thought were good on the basis of lack of compatibility with emerging international standards (with which the Bell System had a tradition at the time of little interest). Thus, they said, as a way of getting even, they had included in the name the diphthong{{sic}} "[[Th_(digraph)#Voiceless_fricative_/θ/|th]]", which of course does not appear in German and several other languages and thus might be difficult for users of those languages to pronounce, which would serve them right.}}

Later, in 2014, after conferring with Asplund, Kerr concluded that the name had likely been invented by Asplund after all:<ref>{{cite web |url=http://dougkerr.net/Pumpkin/articles/Octatherp-octotherp.pdf|author=Douglas A. Kerr |title=The names “octatherp” and “octotherp” for the symbol “#” |date=2014-10-08 }}</ref>

{{quote|Lauren Asplund, at the time a member of the data communications marketing group at the AT&T headquarters in New York City, with his AT&T headquarters engineering counterpart (whose name neither of us can recall) [...] devised the name “octotherp”. He tells me that the inspiration for “octo” was the eight free ends of the four strokes in the symbol. “Therp” did not have any logical premise, but just sounded sort of “Greek-ish”, and thus might confer some scientific stature upon the name. [...] Shortly after this had happened, John Schaak, an office mate of Asplund’s, and a long time personal friend of mine, called me and said that he had a gift for me. [...] the name "octatherp".}}

''The Merriam-Webster New Book of Word Histories'' (1991), has a long article (largely consistent with Doug Kerr's later essay) which says "octotherp" was the original spelling, and that the word arose in the 1960s among telephone engineers as a joke. It concludes, after dismissing various other parochial theories:<ref>{{cite dictionary |title=The Merriam-Webster New Book of Word Histories |date=1991 |entry=octothorp |page=325 |url=https://archive.org/details/merriamwebsterne00merr/page/325/mode/1up?q=octothorp}}</ref>

{{quote|How ''octotherp'' was coined is still a mystery, though we are told by a correspondent from the engineering community that it was coined as a [[wikt:lark around|
lark]], ''octo-'' for 'eight' as previously mentioned, and ''-therp'' when somebody burped. Such a tall-sounding tale is not entirely out of the question, given the arbitrariness of some modern scientific coinages.}}

Other hypotheses for the origin of the word include the last name of [[James Oglethorpe]].<ref>John Baugh, Robert Hass, Maxine H. Kingston, et al., "Octothorpe", ''The American Heritage Dictionary of the English Language'' (Boston: Houghton Mifflin, 2000)</ref> 

The first appearance of ''octothorp'' in a US patent is in a 1973 filing. This patent also refers to the complementary [[telephone star key]] as "the [[sextile]] or asterisk (*) key".<ref name="patent">{{cite web |last1=Lenaerts |first1=George Victor |last2=Auzins |first2=Eric Egils |title=Telephone data set including visual display means |url=https://patents.google.com/patent/US3920926A/en?oq=US3920926 |website=Google Patents |access-date=17 December 2025 |language=en |date=18 November 1975}} The original text, reproduced directly via a scan, and thus of increased accuracy, is available at https://patentimages.storage.googleapis.com/4c/d1/4b/cc45cff01516bf/US3920926.pdf</ref>

===Sharp===
Use of the name ''sharp'' is due to the symbol's resemblance to {{unichar|266F|nlink=}}. The same derivation is seen in the name of the [[Microsoft]] programming languages [[C Sharp (programming language)|C#]], [[J Sharp|J#]] and [[F Sharp (programming language)|F#]]. Microsoft says that the name ''C#'' is pronounced 'see sharp'".<ref>{{cite web |url=https://learn.microsoft.com/en-us/dotnet/csharp/tour-of-csharp/ |title=A tour of the C# language |date=5 April 2023 |access-date=4 April 2024 |website=learn.microsoft.com |archive-date=8 March 2024 |archive-url=https://web.archive.org/web/20240308153937/https://learn.microsoft.com/en-us/dotnet/csharp/tour-of-csharp/ |url-status=live }}</ref> According to the ECMA-334 C# Language Specification, the name of the language is written "C#" ("{{resize|LATIN CAPITAL LETTER C}} (U+0043) followed by the {{resize|NUMBER SIGN}} # (U+0023)") and pronounced "C Sharp".<ref>{{cite book |url=https://ecma-international.org/wp-content/uploads/ECMA-334_7th_edition_december_2023.pdf |title=ECMA-334 C# language specification |edition=7th |publisher=[[Ecma International]] |page=xxiii |chapter=Introduction |date=December 2023 |access-date=4 April 2024 |archive-date=16 December 2023 |archive-url=https://web.archive.org/web/20231216004437/https://ecma-international.org/wp-content/uploads/ECMA-334_7th_edition_december_2023.pdf |url-status=live }}</ref>

===Square===
[[File:Detail-Tastatur-FeTAp-751-1982.JPG|thumb|right|Detail of a telephone keypad displaying the [[Viewdata]] square]]
On telephones, the [[International Telecommunication Union]] specification [[E.161|ITU-T E.161]] 3.2.2 states: "The symbol may be referred to as the square or the most commonly used equivalent term in other languages."<ref>{{cite web | url = http://www.itu.int/rec/T-REC-E.161-200102-I/en | title = E.161 : Arrangement of digits, letters and symbols on telephones and other devices that can be used for gaining access to a telephone network | publisher = [[International Telecommunication Union]] | date = 2 February 2001 | access-date = 23 December 2019 | archive-date = 2 November 2019 | archive-url = https://web.archive.org/web/20191102055736/https://www.itu.int/rec/T-REC-E.161-200102-I/en | url-status = live }}</ref> Formally, this is not a number sign but rather another character, {{unichar|2317|nlink=}}. The real or virtual keypads on almost all modern telephones use the simple {{code|#}} instead, as does most documentation.{{cn|date=January 2023}}

== Usage ==
When {{char|#}} prefixes a number, it is read as 'number'. "A #2 pencil", for example, indicates "a number-two pencil". This usage is historically rarer in print than the abbreviation {{notatypo|'No.'}}<ref name=ngram1>
{{cite web |title=Google Books Ngram Viewer: # 1,No. 1 |url=https://books.google.com/ngrams/graph?content=%23+1%2CNo.+1&year_start=1800&year_end=2022&corpus=en&smoothing=0&case_insensitive=false |website=books.google.com |access-date=30 January 2026 |language=en}}
</ref>{{better source needed|date=January 2026}}, although '#' has recently overtaken 'No.' in total popularity worldwide,<ref name=ngram1/> stemming from its newfound relatively overwhelming popularity in [[American English]]<ref name=ngram-us>
{{cite web |title=Google Books Ngram Viewer: # 1,No. 1 (American English) |url=https://books.google.com/ngrams/graph?content=%23+1%2CNo.+1&year_start=1800&year_end=2022&corpus=en-US&smoothing=0&case_insensitive=false |website=books.google.com |access-date=30 January 2026 |language=en}}
</ref> (but not [[British English]]<ref name=ngram-gb>
{{cite web |title=Google Books Ngram Viewer: # 1,No. 1 (British English) |url=https://books.google.com/ngrams/graph?content=%23+1%2CNo.+1&year_start=1800&year_end=2022&corpus=en-GB&smoothing=0&case_insensitive=false |website=books.google.com |access-date=30 January 2026 |language=en}}
</ref>). In addition to 'No.' and '#', the symbol {{notatypo|'[[№]]'}} or just the word 'number' are also used.<ref>
{{cite web |title=Google Books Ngram Viewer:# 1,№ 1,number 1 |url=https://books.google.com/ngrams/graph?content=%23+1%2C%E2%84%96+1%2Cnumber+1&year_start=1800&year_end=2022&corpus=en&smoothing=0&case_insensitive=false |website=books.google.com |access-date=30 January 2026 |language=en}}
</ref> When used in this manner, # is often [[superscript]], like: "a <sup>#</sup>2 pencil"{{Citation needed|date=January 2026}} — but typically not extending above the [[cap line]].{{Citation needed|date=January 2026}}

When {{angbr|#}} is ''after'' a number, it is read as 'pound' or 'pounds', meaning the unit of weight.<ref>{{Cite web |title=Number Sign/Hashtag - Punctuation {{!}} Ultius |url=https://www.ultius.com/glossary/grammar/punctuation/number-signhashtag |access-date=2025-06-05 |website=www.ultius.com}}</ref><ref>{{Cite web |title=Language Log » The "pound sign" mystery |url=https://languagelog.ldc.upenn.edu/nll/?p=2461 |access-date=2025-06-05}}</ref> The text "5# bag of flour" would mean "five-pound bag of flour". This is rare outside North America.

=== Mathematics ===
* In [[set theory]], #''S'' is one possible notation for the [[cardinality]] or size of the [[set (mathematics)|set]] ''S'', instead of <math>|S|</math>. That is, for a set <math>S = \{s_1,s_2,s_3, \dots , s_n\}</math>, in which all <math>s_i</math> are mutually distinct, <math>\#S = n = |S|.</math> This notation is only sometimes used for [[finite set]]s, usually in [[number theory]], to avoid confusion with the [[divisibility]] symbol, e.g. <math>a \mid b</math>.
* In [[topology]], ''A''#''B'' is the [[connected sum]] of [[manifold]]s ''A'' and ''B'', or of knots ''A'' and ''B'' in [[knot theory]].
* In [[number theory]], ''n''# is the [[primorial]] of ''n''.
* In [[constructive mathematics]], # denotes an [[apartness relation]].
* In [[computational complexity theory]], [[♯P|#P]] denotes a [[complexity class]] of [[counting problem (complexity)|counting problems]]. The standard notation for this class uses the number sign symbol, not the [[sharp sign]] from music, but it is pronounced "sharp P". More generally, the number sign may be used to denote the class of counting problems associated with any class of search problems.

=== Computing ===
{{more citations|section|date=January 2026}}
* In [[Unicode]] and [[ASCII]], the symbol has a [[code point]] as {{unichar|0023}} and [[entity code]] {{code|&num;}} in [[HTML5]].<ref>HTML5 is the only version of HTML that has a named entity for the number sign, see https://www.w3.org/TR/html4/sgml/entities.html {{Webarchive|url=https://web.archive.org/web/20180401051616/http://www.w3.org/TR/html4/sgml/entities.html |date=2018-04-01 }} ("The following sections present the complete lists of character entity references.") and https://www.w3.org/TR/2014/CR-html5-20140731/syntax.html#named-character-references {{Webarchive|url=https://web.archive.org/web/20170805013240/http://www.w3.org/TR/2014/CR-html5-20140731/syntax.html#named-character-references |date=2017-08-05 }} ("num;").</ref>
* In many scripting languages and data file formats, especially ones that originated on Unix, {{code|#}} introduces a comment that goes to the end of the line.<ref name="hash character">{{cite web |title=CSS Syntax and Selectors |url=https://www.w3schools.com/css/css_syntax.asp |website=W3Schools |access-date=2019-07-15 |archive-date=2019-07-12 |archive-url=https://web.archive.org/web/20190712051145/https://www.w3schools.com/css/css_syntax.asp |url-status=live }}</ref> The combination {{code|#!}} at the start of an executable file is a ''[[Shebang (Unix)|shebang]]'', ''hash-bang'' or ''pound-bang'', used to tell the operating system which program to use to run the script (see [[Magic number (programming)|magic number]]). This combination was chosen so it would be a comment in the scripting languages.
* In the [[C preprocessor]] (used by [[C (programming language)|C]] and many other languages), {{code|#}} at the start of a line starts a preprocessor [[Directive (programming)|directive]]. Inside macros (after {{code|#define}}) it is used for various purposes; for example {{code|##}} is used for token [[concatenation]].
* In [[Unix shell]]s, {{code|#}} is placed by convention at the end of a [[command prompt]] to denote that the user is working as [[Superuser|root]].
* {{code|#}} is used in a [[URL]] of a [[web page]] or other resource to introduce a '[[fragment identifier]]'{{snd}} an id which defines a position within that resource. In HTML, this is known as an [[HTML element#Anchor|anchor link]]. For example, in the URL {{code|https://en.wikipedia.org/wiki/Number_sign#Computing}} the portion after the {{code|#}} ({{code|Computing}}) is the fragment identifier, in this case denoting that the display should be moved to show the tag marked by {{code|1=<span id="Computing">...</span>|2=html}} in the HTML.<ref>{{cite web|url=http://www.w3.org/TR/html4/intro/intro.html#fragment-uri|title=Introduction to HTML|access-date=16 September 2014|archive-date=16 August 2008|archive-url=https://web.archive.org/web/20080816014507/http://www.w3.org/TR/html4/intro/intro.html#fragment-uri|url-status=live}}</ref>
* [[Internet Relay Chat]]: on (IRC) servers, {{code|#}} precedes the name of every [[IRC channels|channel]] that is available across an entire IRC network.
* In [[lightweight markup language]]s, such as [[wiki]]text, {{code|#}} is often used to introduce numbered list items.
* In the [[Perl]] programming language, {{code|#}} is used as a modifier to array syntax to return the index number of the last element in the [[Array data type|array]], e.g., an array's last element is at {{code|$array[$#array]}}. The number of elements in the array is {{code|$#array + 1}}, since Perl arrays default to using zero-based indices. If the array has not been defined, the return is also undefined. If the array is defined but has not had any elements assigned to it, e.g., {{code|1=@array = ()}}, then {{code|$#array}} returns {{code|−1}}. See the section on [[Perl language structure#Array functions|Array functions]] in the Perl language structure article.
* {{code|#}} is used in the [[Modula-2]] and [[Oberon (programming language)|Oberon]] programming languages designed by [[Niklaus Wirth]] and in the [[Component Pascal]] language derived from Oberon to denote the ''not equal'' symbol, as a stand-in for the mathematical unequal sign {{char|≠}}, being more intuitive than {{code|<>}} or {{code|1=!=}}. For example: {{nowrap|{{code|IF i # 0 THEN ...|cp}}}}
* In [[Rust (programming language)|Rust]], {{code|#}} is used for attributes such as in {{code|#[test]}}.
* In [[OCaml]], {{code|#}} is the operator used to call a method.
* In [[Common Lisp]],<ref>{{cite web|url=http://www.lispworks.com/documentation/HyperSpec/Body/02_dh.htm|title=Lispworks.com|access-date=16 September 2014|archive-date=10 October 2014|archive-url=https://web.archive.org/web/20141010014731/http://www.lispworks.com/documentation/HyperSpec/Body/02_dh.htm|url-status=live}}</ref> {{code|#}} is a dispatching [[Lisp reader|read macro]] character used to extend the [[S-expression]] syntax with short cuts and support for various data types ([[complex number]]s, vectors and more).
* In [[Scheme (programming language)|Scheme]], {{code|#}} is the prefix for certain syntax with special meaning.
* In [[Standard ML]], {{code|#}}, when prefixed to a field name, becomes a projection function (function to access the field of a record or tuple); also, {{code|#}} prefixes a [[string literal]] to turn it into a character literal.
* In [[Wolfram Mathematica|Mathematica]] syntax, {{code|#}}, when used as a variable, becomes a pure function (a placeholder that is mapped to any variable meeting the conditions).
* In [[LaTeX]], {{code|#}}, when prefixing a number, references an arguments for a user defined command. For instance <syntaxhighlight lang="tex" inline>\newcommand{\code}[1]{\texttt{#1}}</syntaxhighlight>.
* In [[Javadoc]],<ref>{{cite web|url=http://download.oracle.com/javase/1.5.0/docs/tooldocs/windows/javadoc.html#@see|title=Oracle.com|access-date=16 September 2014|archive-date=28 October 2011|archive-url=https://web.archive.org/web/20111028092204/http://download.oracle.com/javase/1.5.0/docs/tooldocs/windows/javadoc.html#@see|url-status=live}}</ref> {{code|#}} is used with the {{code|@see}} tag to introduce or separate a field, constructor, or method member from its containing class.
* In [[Core War|Redcode]] and some other dialects of [[assembly language]], {{code|#}} is used to denote immediate mode addressing, e.g., {{code|LDA #10}}, which means "load accumulator A with the value 10" in [[MOS 6502]] assembly language.
* in [[HTML]], [[Cascading Style Sheets|CSS]], [[Scalable Vector Graphics|SVG]], and other computing applications {{code|#}} is used to identify a color specified in [[hexadecimal]] format, e.g., {{code|#FFAA00}}. This usage comes from [[X11]] color specifications, which inherited it from early assembler dialects that used {{code|#}} to prefix hexadecimal constants, e.g.: ZX Spectrum [[Zilog Z80|Z80]] assembly.<ref>{{cite web|url=http://www.worldofspectrum.org/pub/sinclair/games-info/h/HiSoftDevpacV3.pdf|title=HISOFT DEVPAC ZX Spectrum Programmer's Manual|website=worldofspectrum.org|access-date=2017-10-03|archive-date=2018-11-12|archive-url=https://web.archive.org/web/20181112231113/http://www.worldofspectrum.org/pub/sinclair/games-info/h/HiSoftDevpacV3.pdf|url-status=live}}</ref>
* In [[Be-Music Script]], every command line starts with {{code|#}}. Lines starting with characters other than {{code|#}} are treated as comments.
* The use of the hash symbol in a [[hashtag]] is a phenomenon conceived by [[Chris Messina (open-source advocate)|Chris Messina]], and popularized by social media network [[Twitter]], as a way to direct conversations and topics amongst users. This has led to an increasingly common tendency to refer to the symbol itself as ''hashtag''.<ref name="Time">{{Cite magazine|url=https://time.com/2870942/hashtag-oed-oxford-english-dictionary/|title=You'll Never Guess the Real Name for a Hashtag|last=Nicks|first=Denver|date=June 13, 2014|magazine=TIME|access-date=May 5, 2016|archive-date=May 11, 2016|archive-url=https://web.archive.org/web/20160511235410/http://time.com/2870942/hashtag-oed-oxford-english-dictionary/|url-status=live}}</ref>
* In programming languages like PL/1 and Assembler used on IBM mainframe systems, as well as JCL (Job Control Language), the {{code|#}} (along with {{code|$}} and {{code|@}}) are used as additional letters in identifiers, labels and data set names.
* In [[J (programming language)|J]], {{code|#}} is the ''Tally'' or ''Count'' function,<ref>{{cite web|url=https://code.jsoftware.com/wiki/Vocabulary/number|title=Vocabulary/number|access-date=November 20, 2019|website=J NuVoc|archive-date=February 14, 2020|archive-url=https://web.archive.org/web/20200214105150/https://code.jsoftware.com/wiki/Vocabulary/number|url-status=live}}</ref> and similarly in [[Lua (programming language)|Lua]], {{code|#}} can be used as a shortcut to get the length of a table, or get the length of a string. Due to the ease of writing {{code|#}} over longer function names, this practice has become standard in the Lua community.
* In Dyalog [[APL (programming language)|APL]], {{code|#}} is a reference to the root [[namespace]] while {{code|##}} is a reference to the current space's parent namespace.
* In [[Ada (programming language)|Ada]], the {{code|#}} character is used in based integer literals, which take the form {{code|base#digits#}}, where {{code|base}} is an integer from 2 to 16 specifying the radix, and {{code|digits}} are the digits valid in that base (0-9, optionally A-F for bases above 10).

=== Other uses ===
{{more citations|section|date=January 2026}}
* [[Algebraic notation (chess)|Algebraic notation for chess]]: A hash after a move denotes [[checkmate]].
* [[American Sign Language]] transcription: The hash prefixing an all-caps word identifies a lexicalized fingerspelled sign, having some sort of blends or letter drops. All-caps words without the prefix are used for standard English words that are fingerspelled in their entirety.<ref>{{cite web |last1=Vicars |first1=Bill |title=Lexicalization |url=http://www.lifeprint.com/asl101/topics/lexicalized_fingerspelling.htm |publisher=ASL University |access-date=6 September 2015 |archive-date=10 September 2015 |archive-url=https://web.archive.org/web/20150910183425/http://www.lifeprint.com/asl101/topics/lexicalized_fingerspelling.htm |url-status=live }}</ref>
* [[copy writer|Copy writing]] and [[copy editing]]: Technical writers in [[press release]]s often use three number signs, {{char|{{vanchor|###}}}} directly above the boilerplate or underneath the body copy, indicating to media that there is no further copy to come.<ref>{{cite web |title=###: What does ### mean at the end of a press release? |publisher=The Halo Group |url=https://www.thehalogroup.com/what-does-mean-at-the-end-of-a-press-release/ |first=Lara |last=Cohn |access-date=18 November 2021 |archive-date=17 November 2021 |archive-url=https://web.archive.org/web/20211117221859/https://www.thehalogroup.com/what-does-mean-at-the-end-of-a-press-release/ |url-status=live }}</ref>
* [[Note (typography)|Footnote]] symbols (or endnote symbols): Due to its ready availability in many computer fonts and directly on computer keyboards, {{code|#}} and other symbols (such as the [[caret]] ({{code|^}})) have in recent years begun to be occasionally used in catalogues and reports in place of more traditional symbols (esp. [[Dagger (mark)|dagger, double-dagger]], [[pilcrow]]).
* Linguistic [[phonology]]: {{char|#}} denotes a word boundary. For instance, {{code|/d/ → [t] / _#}} means that {{char|/d/}} becomes {{char|[t]}} when it is the last segment in a word (i.e. when it appears before a word boundary).
* Linguistic [[syntax]]: A hash before an example sentence denotes that the sentence is semantically ill-formed, though grammatically well-formed. For instance, "#The toothbrush is pregnant" is a grammatically correct sentence, but the meaning is odd.<ref>{{cite book|last=Carnie|first=Andrew|year=2006|title=Syntax: A Generative Introduction|location=Oxford|publisher=Wiley-Blackwell|isbn=1-4051-3384-8|edition=2nd|url-access=registration|url=https://archive.org/details/syntaxgenerative0000carn}}</ref><ref>{{Cite book | first=R. L. | last=Trask | author-link=Larry Trask | title=A Dictionary of Grammatical Terms in Linguistics | location=London | publisher=Routledge | year=1993 | isbn=0-415-08627-2 | page=125}}</ref>
* [[Medical prescription]] drug delimiter: In some countries, such as [[Norway]] or [[Poland]], {{char|#}} is used as a [[delimiter]] between different drugs on medical prescriptions.
* Medical shorthand: The hash is often used to indicate a [[bone fracture]].<ref>{{Cite web |url=http://radiographics.rsnajnls.org/cgi/reprint/23/1/195.pdf |title=Glossary of Medical Devices and Procedures: Abbreviations, Acronyms, and Definitions |access-date=2008-05-16 |archive-date=2008-06-25 |archive-url=https://web.archive.org/web/20080625213552/http://radiographics.rsnajnls.org/cgi/reprint/23/1/195.pdf |url-status=live }}</ref> For example, {{code|#NOF}} is often used for "fractured [[Femur neck|neck of femur]]". In radiotherapy, a full dose of radiation is divided into smaller doses or 'fractions'. These are given the shorthand {{char|#}} to denote either the number of treatments in a prescription (e.g. {{code|60Gy in 30#}}), or the fraction number ({{code|#9 of 25}}).
* As a [[List of proofreader's marks|proofreading mark]], to indicate that a space should be inserted.<ref>{{cite web |url=http://www.merriam-webster.com/mw/table/proofrea.htm |title=Proofreaders' Marks |access-date=2020-09-03 |archive-date=2010-08-16 |archive-url=https://web.archive.org/web/20100816210104/http://www.merriam-webster.com/mw/table/proofrea.htm |url-status=dead }} from [[Merriam Webster]]</ref>
* Publishing: When submitting a science fiction manuscript for publication, a number sign on a line by itself (indented or centered)  indicates a [[Section (typography)|section break]] in the text.<ref>{{cite web|url=http://www.sfwa.org/wp-content/uploads/2009/06/Mssprep.pdf|title=Manuscript Preparation|last=McIntyre|first=Vonda|date=October 2008|website=sfwa.org|publisher=Science Fiction & Fantasy Writers of America|access-date=28 May 2020|archive-date=3 October 2020|archive-url=https://web.archive.org/web/20201003095936/http://www.sfwa.org/wp-content/uploads/2009/06/Mssprep.pdf|url-status=live}}</ref>
* [[Scrabble]]: Putting a number sign after a word indicates that the word is found in the British word lists, but not the [[Official Tournament and Club Word List|North American lists.]]<ref>{{cite web|url=http://www.tucsonscrabble.com/articles/glossary.html|title=Scrabble Glossary|publisher=Tucson Scrabble Club|access-date=2012-02-06|archive-url=https://web.archive.org/web/20110830073348/http://www.tucsonscrabble.com/articles/glossary.html|archive-date=2011-08-30|url-status=dead}}</ref>
* [[Teletext]] and [[Digital Video Broadcasting|DVB]] [[subtitle]]s (in the UK and Ireland): The hash symbol, resembling music notation's sharp sign, is used to mark text that is either sung by a character or heard in background music, e.g. {{mono|''#&nbsp;For he's a jolly good fellow&nbsp;#''}}

==Unicode==

The number sign was assigned code 35 (hex 0x23) in ASCII where it was inherited by many character sets. In [[EBCDIC]] it is often at 0x7B or 0xEC.

Unicode characters with 'number sign' in their names:
* {{unichar|0023}} (Other [[Unicode character property|attested names in Unicode]] are: {{sc|pound sign (weight), hashtag, hash, crosshatch, octothorpe}}.<ref>{{cite web |author=Unicode Consortium |title=C0 Controls and Basic Latin| url=https://www.unicode.org/charts/PDF/U0000.pdf}}</ref>)
* {{unichar|0600|html=|nlink=}}
* {{unichar|0BFA|html=|nlink=}}
* {{unichar|1AC6|nlink=}}
* {{unichar|FE5F}}
* {{unichar|FF03}}
* {{unichar|110BD|nlink=}}
* {{unichar|110CD|nlink=}}
* {{unichar|11FE9|nlink=}}
* {{unichar|E0023|nlink=}}

Additionally, a Unicode named sequence {{resize|KEYCAP NUMBER SIGN}} is defined for the [[grapheme cluster]] {{code|U+0023+FE0F+20E3}} (#️⃣).<ref>{{cite web |url=https://www.unicode.org/Public/UCD/latest/ucd/NamedSequences.txt |title=Unicode Named Character Sequences |work=Unicode Character Database |author=Unicode Consortium |author-link=Unicode Consortium |access-date=2020-07-16 |archive-date=2020-07-11 |archive-url=https://web.archive.org/web/20200711232858/http://www.unicode.org/Public/UCD/latest/ucd/NamedSequences.txt |url-status=live}}</ref>{{efn|{{unichar|0023}}, {{unichar|FE0F|nlink=}}, {{unichar|20E3|nlink=}} }}

==On keyboards==
On the standard [[QWERTY|US keyboard layout]], the {{char|#}} symbol is {{keypress|Shift|3}}. On standard UK and some other European keyboards, the same keystrokes produce the [[Pound sign|pound (sterling) sign, {{char|£}} symbol]], and {{keypress|#}} may be moved to a separate key above the right shift key.

==See also==
{{Wiktionary|number sign}}
* {{unichar|266F|nlink=}}
* {{unichar|2317|nlink=}}
* {{unichar|22D5|nlink=}}
* {{unichar2|⌘|nlink=}} ("looped square")
* {{unichar|4E95|nlink=井 (disambiguation)}}, the [[Chinese character]] for a well ({{Zh-cjp|c=[[wiktionary:井|井]]|p=jǐng|j=zeng2}})
* the game [[tic-tac-toe]], which uses a similar grid pattern 

{{For|uses of # within Wikipedia|Wikipedia:Number sign}}

== Explanatory notes ==
{{Notelist}}

==References==
{{Reflist|2}}

{{navbox punctuation}}
[[Category:Latin-script ligatures]]
[[Category:Typographical symbols]]