Number sign
Number sign is a name for the symbol #, which is used for a variety of purposes including, in some countries, the designation of a number (for example, "#1" stands for "number one"). The symbol is in Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

 as code point
Code point
In character encoding terminology, a code point or code position is any of the numerical values that make up the code space . For example, ASCII comprises 128 code points in the range 0hex to 7Fhex, Extended ASCII comprises 256 code points in the range 0hex to FFhex, and Unicode comprises 1,114,112...

 ; it is also present in ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 with the same value.

In Commonwealth English
Commonwealth English
The use of the English language in most member countries of the Commonwealth of Nations was inherited from British colonisation. English is spoken as a first or second language in most of the Commonwealth. In a few countries, such as Cyprus and Malaysia, it does not have official status, but is...

, the symbol is usually called the hash and the corresponding telephone key is called the hash key. In American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

, the symbol is usually called the pound sign (outside the US, this term often refers instead to the British currency symbol "£"
Pound sign
The pound sign is the symbol for the pound sterling—the currency of the United Kingdom . The same symbol is used for similarly named currencies in some other countries and territories, such as the Irish pound, Gibraltar pound, Australian pound and the Italian lira...

) and the telephone key is called the pound key. In Canadian English
Canadian English
Canadian English is the variety of English spoken in Canada. English is the first language, or "mother tongue", of approximately 24 million Canadians , and more than 28 million are fluent in the language...

, this key is most frequently called the number sign key. Beginning in the 1960s, telephone engineers have attempted to coin a special name for this symbol, with variant spellings including octothorp, octothorpe, octathorp, octotherp, octathorpe, and octatherp; none of these has become widely accepted.

In many parts of the world, including Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, Canadian French
Canadian French
Canadian French is an umbrella term referring to the varieties of French spoken in Canada. French is the mother tongue of nearly seven million Canadians, a figure constituting roughly 22% of the national population. At the federal level it has co-official status alongside English...

, Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, and parts of Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, number sign (or equivalents in local languages) refers instead to the numero sign ("№")
Numero sign
The numero sign or numero symbol is a typographic abbreviation of the word number indicating ordinal numeration, especially in names and titles...


The symbol is easily confused with the musical symbol called sharp
Sharp (music)
In music, sharp, dièse , or diesis means higher in pitch and the sharp symbol raises a note by a half tone. Intonation may be flat, sharp, or both, successively or simultaneously...

 (). In both symbols, there are two pairs of parallel lines. The key difference is that the number sign has true horizontal strokes while the sharp sign has two slanted parallel lines which must rise from left-to-right, in order to avoid being confused with the musical staff lines. Both signs may have true vertical lines; however, they are compulsory in the sharp sign, but optional in the number sign (#) depending on typeface
In typography, a typeface is the artistic representation or interpretation of characters; it is the way the type looks. Each type is designed and there are thousands of different typefaces in existence, with new ones being developed constantly....

 or handwriting
Handwriting is a person's particular & individual style of writing with pen or pencil, which contrasts with "Hand" which is an impersonal and formalised writing style in several historical varieties...

 style. Thus, only the number sign may have an italic
Italic type
In typography, italic type is a cursive typeface based on a stylized form of calligraphic handwriting. Owing to the influence from calligraphy, such typefaces often slant slightly to the right. Different glyph shapes from roman type are also usually used—another influence from calligraphy...


Usage and naming conventions in North America

Mainstream use in the US as follows: when it precedes a number, it is read as "number", as in "a #2 pencil" (spoken aloud as: "a number two pencil").

In the United States, the symbol is traditionally called the pound sign. The pound name derives from a series of abbreviations for pound
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

, the unit of weight. At first "lb." was used; however, printers later designed a font containing a special symbol of an "lb" with a line through the verticals so that the lowercase letter "l" would not be mistaken for the numeral/digit "1". Unicode character U+2114 is called the "L B bar symbol", and it is a cursive
Cursive, also known as joined-up writing, joint writing, or running writing, is any style of handwriting in which the symbols of the language are written in a simplified and/or flowing manner, generally for the purpose of making writing easier or faster...

 development of this symbol. Ultimately, the symbol was reduced for clarity as an overlay of two horizontal strokes "=" across two forward-slash-like strokes "//". Keith Gordon Irwin, in The Romance of Writing p. 125, says: "The Italian libbra (from the old Latin word libra, 'balance') represented a weight almost exactly equal to the avoirdupois
The avoirdupois system is a system of weights based on a pound of 16 ounces. It is the everyday system of weight used in the United States and is still widely used to varying degrees by many people in Canada, the United Kingdom, and some other former British colonies despite the official adoption...

 pound of England. The Italian abbreviation of lb with a line drawn across the letters [℔] was used for both weights. The business clerks' hurried way of writing the abbreviation appears to have been responsible for the # sign used for pound."

In Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, the symbol is traditionally referred to as the number sign. Major telephone equipment manufacturers, such as Nortel
Nortel Networks Corporation, formerly known as Northern Telecom Limited and sometimes known simply as Nortel, was a multinational telecommunications equipment manufacturer headquartered in Mississauga, Ontario, Canada...

, have an option in their programming to denote Canadian pronunciation, which in turn instructs the system to say "number sign" to callers instead of "pound sign." This same option causes the system to say "zed" instead of the United States' "zee" for the letter Z.

Usage in the UK and Ireland

In the UK and Ireland, the symbol is most often called the hash. It is never used to refer to pounds weight (lb is commonly used for this) or to pounds sterling (where "£" is used). It is never called the "pound sign" since that term is understood to mean the currency symbol "£
Pound sign
The pound sign is the symbol for the pound sterling—the currency of the United Kingdom . The same symbol is used for similarly named currencies in some other countries and territories, such as the Irish pound, Gibraltar pound, Australian pound and the Italian lira...

", for pound sterling
Pound sterling
The pound sterling , commonly called the pound, is the official currency of the United Kingdom, its Crown Dependencies and the British Overseas Territories of South Georgia and the South Sandwich Islands, British Antarctic Territory and Tristan da Cunha. It is subdivided into 100 pence...

 or (formerly) Irish pound
Irish pound
The Irish pound was the currency of Ireland until 2002. Its ISO 4217 code was IEP, and the usual notation was the prefix £...


The use of "#" as an abbreviation for "number" is uncommon in Britain, to the extent that many people would not even recognise the usage. Where Americans might write "Symphony #5", the British are more likely to write "Symphony No. 5".

To add to the confusion between "£" and "#", in BS 4730 (the UK national variant of the ISO/IEC 646
ISO/IEC 646:1991, Information technology — ISO 7-bit coded character set for information interchange, is an ISO standard that since its first edition in 1972 has specified a 7-bit character code from which several national standards are derived...

 character set), 0x23 represents "£" whereas in ASCII (the US variant), it represents "#". It was thus common, when systems were incorrectly configured, for "£" to be displayed as "#" or vice versa.

Other names in English

The symbol has many other names (and uses) in English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...


Comment sign : Taken from its use in many shell script
Shell script
A shell script is a script written for the shell, or command line interpreter, of an operating system. It is often considered a simple domain-specific programming language...

s and some programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

s (such as Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...

) to start comment
Comment (computer programming)
In computer programming, a comment is a programming language construct used to embed programmer-readable annotations in the source code of a computer program. Those annotations are potentially significant to programmers but typically ignorable to compilers and interpreters. Comments are usually...

Cross : In China, non-native English speakers often refer to the number sign as "cross". It is said as jing in Chinese, as it looks like the Chinese character for water well ("井").
Hex : Common usage in Singapore and Malaysia, as spoken by many recorded telephone directory-assistance menus: 'Please enter your phone number followed by the hex (sic
Sic—generally inside square brackets, [sic], and occasionally parentheses, —when added just after a quote or reprinted text, indicates the passage appears exactly as in the original source...

: number sign) key'. The term 'hex' is discouraged in Singapore in favour of 'hash'.
Octothorp, octothorpe, octathorp, octatherp
Used by Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...

 engineers by 1968. Lauren Asplund, who provided the article, says that he and a colleague were the source of octothorp at AT&T engineering in New York in 1964. The Merriam-Webster New Book of Word Histories, 1991, has a long article that is consistent with Doug Kerr's essay, in that it says "octotherp" was the original spelling, and that the word arose in the 1960s among telephone engineers as a joke. The first appearance of "octothorp" in a US patent is in a 1973 filing which also refers to the six-pointed asterisk (*) used on telephone buttons as a "sextile".

Sharp (music)
In music, sharp, dièse , or diesis means higher in pitch and the sharp symbol raises a note by a half tone. Intonation may be flat, sharp, or both, successively or simultaneously...

 : Resemblance to the glyph used in music notation, U+266F
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

 (♯). So called in the name of the Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 programming languages C# and F#. However Microsoft says "It's not the 'hash' (or pound) symbol as most people believe. It's actually supposed to be the musical sharp symbol. However, because the sharp symbol is not present on the standard keyboard, it's easier to type the hash ('#') symbol. The name of the language is, of course, pronounced 'see sharp'." According to the ECMA-334 C# Language Specification, section 6, Acronyms and abbreviations, the name of the language is written "C#" ("LATIN CAPITAL LETTER C (U+0043) followed by the NUMBER SIGN # (U+0023)") and pronounced "C Sharp".
: Used by editors to denote where space should be inserted in a galley proof
Galley proof
In printing and publishing, proofs are the preliminary versions of publications meant for review by authors, editors, and proofreaders, often with extra wide margins. Galley proofs may be uncut and unbound, or in some cases electronic...

. This can mean
  1. a line space (the space between two adjacent lines denoted by line # in the margin),
  2. a hair space (the space between two letters in a word, denoted by hr #)
  3. a word space, or letter space (the space between two words on a line, two letter spaces being ##)
Em- and en-spaces (being the length of a letter m and n, respectively) are denoted by a square-shaped em- or en-quad character ( and , respectively).

Square : Occasionally used in the UK (e.g. sometimes in BT
BT Group
BT Group plc is a global telecommunications services company headquartered in London, United Kingdom. It is one of the largest telecommunications services companies in the world and has operations in more than 170 countries. Through its BT Global Services division it is a major supplier of...

 publications and automatic messages) – especially during the Prestel
Prestel , the brand name for the UK Post Office's Viewdata technology, was an interactive videotex system developed during the late 1970s and commercially launched in 1979...

 era, when the symbol was a page address delimiter. The International Telecommunications Union specification ITU-T E.161
E.161 is an ITU-T recommendation that defines the assignment of the basic 26 Latin letters to the 12-key telephone keypad. Uses for this mapping include:* Multi-tap and predictive text systems* Forming phonewords from telephone numbers...

 3.2.2 states: "The # is to be known as a 'square' or the most commonly used equivalent term in other languages."
Crunch : It is used as "crunch" in the Linux distribution #! "Crunch Bang" (
Others : crosshatch, (garden) fence, mesh, flash, grid, pig-pen, tictactoe, scratch (mark), (garden) gate, hak, oof, rake, sink, corridor, unequal, punch mark.

In mathematics

  • In set theory
    Set theory
    Set theory is the branch of mathematics that studies sets, which are collections of objects. Although any type of object can be collected into a set, set theory is applied most often to objects that are relevant to mathematics...

    , #S is the cardinality of the set S. That is, for a set #S = n.
  • In topology
    Topology is a major area of mathematics concerned with properties that are preserved under continuous deformations of objects, such as deformations that involve stretching, but no tearing or gluing...

    , where A and B are manifolds, A#B is the manifolds' connected sum
    Connected sum
    In mathematics, specifically in topology, the operation of connected sum is a geometric modification on manifolds. Its effect is to join two given manifolds together near a chosen point on each...

    . In knot theory
    Knot theory
    In topology, knot theory is the study of mathematical knots. While inspired by knots which appear in daily life in shoelaces and rope, a mathematician's knot differs in that the ends are joined together so that it cannot be undone. In precise mathematical language, a knot is an embedding of a...

     (a branch of topology), where A and B are knots, A#B is the knots' knot sum.
  • In number theory
    Number theory
    Number theory is a branch of pure mathematics devoted primarily to the study of the integers. Number theorists study prime numbers as well...

    , n# is the primorial
    In mathematics, and more particularly in number theory, primorial is a function from natural numbers to natural numbers similar to the factorial function, but rather than multiplying successive positive integers, only successive prime numbers are multiplied...

     of n.

In computing

  • # is one of the two standard special keys beyond digits 0 to 9 on a telephone keypad
    Telephone keypad
    A telephone keypad is a keypad that appears on a "Touch Tone" telephone. It was standardised when the dual-tone multi-frequency system in the new push-button telephone was introduced in the 1960s, which gradually replaced the rotary dial....

     (the other being the star key, *). It generates a compound tone mixing 941 Hz and 1477 Hz. Its function depends on services provided by a given telephone-based service, but it is often used to denote the end of a variable-length number such as an account number or item number.
  • In many scripting languages and data file formats, especially ones that originated on Unix
    Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

    , the # introduces a comment
    Comment (computer programming)
    In computer programming, a comment is a programming language construct used to embed programmer-readable annotations in the source code of a computer program. Those annotations are potentially significant to programmers but typically ignorable to compilers and interpreters. Comments are usually...

     that goes to the end of the line. The combination #! at the start of an executable file is a "shebang
    Shebang (Unix)
    In computing, a shebang is the character sequence consisting of the characters number sign and exclamation point , when it occurs as the first two characters on the first line of a text file...

    " or "hash-bang", used to tell the operating system
    Operating system
    An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

     which program to use to run the script (see magic number
    Magic number (programming)
    In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:* A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures...

    ). This combination was chosen so it would be a comment in the scripting languages.
  • In the C preprocessor
    C preprocessor
    The C preprocessor is the preprocessor for the C and C++ computer programming languages. The preprocessor handles directives for source file inclusion , macro definitions , and conditional inclusion ....

     (and the C++
    C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...

     preprocessor, and other syntactically C-like languages), # is used to start a preprocessor directive. Inside macros (after #define) it is used for various purposes, including the double pound sign ## used for token concatenation.
  • In Unix shells, # is placed by convention at the end of a command prompt to denote that the user is working as root.
  • # is used in a URL
    Uniform Resource Locator
    In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....

     of a webpage or other resource to introduce a "fragment identifier
    Fragment identifier
    In computer hypertext, a fragment identifier is a short string of characters that refers to a resource that is subordinate to another, primary resource...

    " – an id which defines a position within that resource. For example, in the URL the portion after the # (In_computing) is the fragment identifier, in this case denoting that the display should be moved to show the tag marked by ... in the HTML
  • Internet Relay Chat
    Internet Relay Chat
    Internet Relay Chat is a protocol for real-time Internet text messaging or synchronous conferencing. It is mainly designed for group communication in discussion forums, called channels, but also allows one-to-one communication via private message as well as chat and data transfer, including file...

    : on (IRC) servers, # precedes the name of every channel that is available across an entire IRC network.
  • In blog
    A blog is a type of website or part of a website supposed to be updated with new content from time to time. Blogs are usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in...

    s, # is sometimes used to denote a permalink
    A permalink is a URL that points to a specific blog or forum entry after it has passed from the front page to the archives. Because a permalink remains unchanged indefinitely, it is less susceptible to link rot. Most modern weblogging and content-syndication software systems support such links...

     for that particular weblog entry.
  • On social networking sites such as Twitter
    Twitter is an online social networking and microblogging service that enables its users to send and read text-based posts of up to 140 characters, informally known as "tweets".Twitter was created in March 2006 by Jack Dorsey and launched that July...

    , # is used to denote a metadata tag
    Tag (metadata)
    In online computer systems terminology, a tag is a non-hierarchical keyword or term assigned to a piece of information . This kind of metadata helps describe an item and allows it to be found again by browsing or searching...

    , or "hashtag".
  • In lightweight markup language
    Lightweight markup language
    A lightweight markup language is a markup language with a simple syntax, designed to be easy for a human to enter with a simple text editor, and easy to read in its raw form....

    s, such as wikitext
    Wikitext language, or wiki markup, is a lightweight markup language used to write pages in wiki websites, such as Wikipedia, and is a simplified alternative/intermediate to HTML. Its ultimate purpose is to be converted by wiki software into HTML, which in turn is served to web browsers.There is no...

    , # is often used to introduce numbered list items.
  • In Objective Caml
    Objective Caml
    OCaml , originally known as Objective Caml, is the main implementation of the Caml programming language, created by Xavier Leroy, Jérôme Vouillon, Damien Doligez, Didier Rémy and others in 1996...

    , # is the operator used to call a method.
  • In Common Lisp
    Common Lisp
    Common Lisp, commonly abbreviated CL, is a dialect of the Lisp programming language, published in ANSI standard document ANSI INCITS 226-1994 , . From the ANSI Common Lisp standard the Common Lisp HyperSpec has been derived for use with web browsers...

     and Scheme, # is the prefix for certain syntax with special meaning.
  • In Standard ML
    Standard ML
    Standard ML is a general-purpose, modular, functional programming language with compile-time type checking and type inference. It is popular among compiler writers and programming language researchers, as well as in the development of theorem provers.SML is a modern descendant of the ML...

    , #, when prefixed to a field name, becomes a projection function (function to access the field of a record or tuple); also, # prefixes a string literal to turn it into a character literal.
  • In Mathematica
    Mathematica is a computational software program used in scientific, engineering, and mathematical fields and other areas of technical computing...

     syntax, #, when used as a variable, becomes a pure function (a placeholder that is mapped to any variable meeting the conditions).
  • In LaTeX
    LaTeX is a document markup language and document preparation system for the TeX typesetting program. Within the typesetting system, its name is styled as . The term LaTeX refers only to the language in which documents are written, not to the editor used to write those documents. In order to...

    , #, when prefixing a number, references an arguments for a user defined command. For instance \newcommand{\code}[1]{\texttt{#1}}.
  • In Javadoc
    Javadoc is a documentation generator from Sun Microsystems for generating API documentation in HTML format from Java source code.The "doc comments" format used by Javadoc is the de facto industry standard for documenting Java classes. Some IDEs, such as Netbeans and Eclipse automatically generate...

    , # is used with the @see tag to introduce or separate a field, constructor, or method member from its containing class.

Other uses

  • Press releases: the notation "###" denotes "end", i.e. that there is no further copy to come.
  • Chess notation
    Chess notation
    Chess notation is the term for several systems that have developed to record either the moves made during a game of chess or the position of the pieces on a chess board. The earliest systems of notation used lengthy narratives to describe each move; these gradually evolved into terser systems of...

    : # after a move denotes checkmate
    Checkmate is a situation in chess in which one player's king is threatened with capture and there is no way to meet that threat. Or, simply put, the king is under direct attack and cannot avoid being captured...

    , being easier to type than the traditional ‡.
  • Prescription drug delimiter: in some countries, such as Norway
    Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

     or Poland
    Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

    , # is used as a delimiter
    A delimiter is a sequence of one or more characters used to specify the boundary between separate, independent regions in plain text or other data streams. An example of a delimiter is the comma character, which acts as a field delimiter in a sequence of comma-separated values.Delimiters represent...

     between different drugs on medical prescription
    Medical prescription
    A prescription is a health-care program implemented by a physician or other medical practitioner in the form of instructions that govern the plan of care for an individual patient. Prescriptions may include orders to be performed by a patient, caretaker, nurse, pharmacist or other therapist....

  • Copy writing and editing: technical writers often use three hash signs ("###") as a marker in text where more content will be added or there are errors to be corrected.
  • Mining
    Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

    : in underground mining, the hash sign is sometimes used as a shorthand for "seam" or "shaft
    Shaft mining
    Shaft mining or shaft sinking refers to the method of excavating a vertical or near-vertical tunnel from the top down, where there is initially no access to the bottom....

    ". An example would be "4#", which would mean "four shaft" or "four seam" depending on the context.
  • Medical shorthand: # is often used as medical shorthand for 'fracture
    Bone fracture
    A bone fracture is a medical condition in which there is a break in the continuity of the bone...

  • In linguistic phonetics
    Phonetics is a branch of linguistics that comprises the study of the sounds of human speech, or—in the case of sign languages—the equivalent aspects of sign. It is concerned with the physical properties of speech sounds or signs : their physiological production, acoustic properties, auditory...

    , # denotes a word boundary. For instance, /d/ -> [t] / _# means that /d/ becomes [t] when it is the last segment in a word (ie. when it appears before a word boundary).
  • In linguistic syntax
    In linguistics, syntax is the study of the principles and rules for constructing phrases and sentences in natural languages....

    , # before an example sentence denotes that the sentence is semantically ill-formed, though grammatically well-formed. For instance, "#The toothbrush is pregnant" is a grammatical sentence, but the meaning is odd.
  • In Teletext
    Teletext is a television information retrieval service developed in the United Kingdom in the early 1970s. It offers a range of text-based information, typically including national, international and sporting news, weather and TV schedules...

     and DVB subtitles
    Subtitle (captioning)
    Subtitles are textual versions of the dialog in films and television programs, usually displayed at the bottom of the screen. They can either be a form of written translation of a dialog in a foreign language, or a written rendering of the dialog in the same language, with or without added...

     in the UK, the # symbol is used to mark text that is sung either by a character or heard in background music. eg. # For he's a jolly good fellow #

On keyboards

On standard US keyboard layout
Keyboard layout
A keyboard layout is any specific mechanical, visual, or functional arrangement of the keys, legends, or key–meaning associations of a computer, typewriter, or other typographic keyboard....

s, the # symbol is . On standard UK and some European keyboards, the same keystrokes produce the pound currency symbol (£), and # is moved to a separate key above the right shift. On UK Mac keyboards, # is generated by , whereas on European Mac keyboards, the # can be found above the right shift key. Under DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...

 and Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

, it can be also generated through the Alt code Alt-35.
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