Number sign

Template:About Template:Short description Template:Infobox symbol The symbol Template:Char is known as the number sign, hash, and the pound sign 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 ligatured abbreviation for pounds avoirdupois – having been derived from the now-rare Template:Char.

Since 2007, widespread usage of the symbol to introduce metadata tags on social media platforms has led to such tags being known as 'hashtags', and from that, the symbol itself is sometimes called a hashtag.

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

History

A stylized version of the abbreviation for Template:Lang (Template:Translation)

The abbreviation written by Isaac Newton, showing the evolution from Template:Char toward Template:Char

It is believed that the symbol traces its origins to the symbol Template:Char,Template:Efn an abbreviation of the Roman term Template:Lang, which translates as "pound weight". The abbreviation lb was printed as the dedicated ligature Template:Char, including a horizontal line across (which indicated abbreviation). Ultimately, the symbol was reduced for clarity as an overlay of two horizontal strokes Template:Char across two slash-like strokes Template:Char.

In printing, a sign similar to Template: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, in Philip Luckombe’s 1770 book on printing or the 1847 revision of Noah Webster’s Dictionary by Chauncey A. Goodrich.

A similar sign (like Template:Char) has also sometimes been used as a sign for the ducat coin, other times included with abbreviations starting with D, or as a substitute for the milréis sign. In some 16th century German accounting manuscripts, the numero sign (Template:Not a typo) is written with an N with two extra lines ornamenting it.. The symbol, printed as Template:Char, is described as the "number" character in an 1853 treatise on bookkeeping, and its double meaning (number, pound) is described in a bookkeeping text from 1880. German language references from 1873 or 1892 also shows the symbol for 'ducat' (Template:Lang) or 'number' (Template:Lang), printed as Template:Char or Template:Char, with number also represented with Template:Char.Template:Efn

The instruction manual of the Blickensderfer model 5 typewriter (Template:Circa) appears to refer to the symbol as the "number mark". Some early-20th-century U.S. sources refer to it as the "number sign". 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). A 1917 manual distinguishes between two uses of the sign: "number (written before a figure)" and "pounds (written after a figure)". The use of the phrase "pound sign" to refer to this symbol is found from 1932 in U.S. usage.

For mechanical devices, the symbol appeared on the keyboard of the Remington Standard typewriter (Template:Circa). 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 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.

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 (IRC) networks circa 1988 to label groups and topics. This usage inspired Chris Messina to propose a similar system to be used on Twitter to tag topics of interest on the microblogging network; this became known as a hashtag. Although used initially and most popularly on Twitter, hashtag use has extended to other social media sites. Template:Anchor

Names

Number sign

Number sign is the name chosen by the Unicode Consortium. Most common in Canada and the northeastern United States.Template:Citation needed 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". 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 No..

Pound sign

In the United States and Canada, the Template: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 Template:Keypress, for example, can be read as "pound seven seven". This name is rarely used elsewhere, as the term pound sign is understood to mean the currency symbol £.

Hash

In the United Kingdom and Australia, it is frequently called a hash (probably from hatch, referring to cross-hatching). This is also called a Template:Wikt-lang or Template:Wikt-lang.

The term hash sign is found in South African writings from the late 1960s.

Programmers also use this term; for instance Template:Code is "hash, bang" or "shebang".

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 Template:Code 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. Twitter documentation referred to it as "the hashtag symbol".

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.Template:Cn In Singapore, the symbol is also called "hex" in apartment addresses, where it precedes the floor number.

Octothorp

Template:Wikt The word octothorpTemplate:Efn or octatherp was invented by workers at the Bell Telephone Laboratories by 1968, who wanted to add an eleventh and a twelfth key to the telephone keypad and needed named symbols to identify them. 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. Lauren Asplund declared that he and Howard Eby invented the word in 1964: Template:Quote

Doug Kerr has written two essays about his recollections on the subject. In the first, in 2006, he wrote: Template:Quote

Later, in 2014, after conferring with Asplund, Kerr concluded that the name had likely been invented by Asplund after all:

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:

Other hypotheses for the origin of the word include the last name of James Oglethorpe.

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".

Sharp

Use of the name sharp is due to the symbol's resemblance to Template:Unichar. The same derivation is seen in the name of the Microsoft programming languages C#, J# and F#. Microsoft says that the name C# is pronounced 'see sharp'". According to the ECMA-334 C# Language Specification, the name of the language is written "C#" ("Template:Resize (U+0043) followed by the Template:Resize # (U+0023)") and pronounced "C Sharp".

Square

Detail of a telephone keypad displaying the Viewdata square

On telephones, the International Telecommunication Union specification 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." Formally, this is not a number sign but rather another character, Template:Unichar. The real or virtual keypads on almost all modern telephones use the simple Template:Code instead, as does most documentation.Template:Cn

Usage

When Template: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 Template:NotatypoTemplate:Better source needed, although '#' has recently overtaken 'No.' in total popularity worldwide, stemming from its newfound relatively overwhelming popularity in American English (but not British English). In addition to 'No.' and '#', the symbol Template:Notatypo or just the word 'number' are also used. When used in this manner, # is often superscript, like: "a ^#2 pencil"Template:Citation needed — but typically not extending above the cap line.Template:Citation needed

When Template:Angbr is after a number, it is read as 'pound' or 'pounds', meaning the unit of weight. 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 S, instead of $|S|$. That is, for a set $S=\{s_1,s_2,s_3,\dots ,s_n\}$, in which all $s_i$ are mutually distinct, $\mathrm{\#}S=n=|S|.$ This notation is only sometimes used for finite sets, usually in number theory, to avoid confusion with the divisibility symbol, e.g. $a\mid b$.
• In topology, A#B is the connected sum of manifolds 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 denotes a complexity class of 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

• In Unicode and ASCII, the symbol has a code point as Template:Unichar and entity code Template:Code in HTML5.
• In many scripting languages and data file formats, especially ones that originated on Unix, Template:Code introduces a comment that goes to the end of the line. The combination Template:Code at the start of an executable file is a shebang, hash-bang or pound-bang, used to tell the operating system which program to use to run the script (see magic number). This combination was chosen so it would be a comment in the scripting languages.
• In the C preprocessor (used by C and many other languages), Template:Code at the start of a line starts a preprocessor directive. Inside macros (after Template:Code) it is used for various purposes; for example Template:Code is used for token concatenation.
• In Unix shells, Template:Code is placed by convention at the end of a command prompt to denote that the user is working as root.
• Template:Code is used in a URL of a web page or other resource to introduce a 'fragment identifier'Template:Snd an id which defines a position within that resource. In HTML, this is known as an anchor link. For example, in the URL Template:Code the portion after the Template:Code (Template:Code) is the fragment identifier, in this case denoting that the display should be moved to show the tag marked by Template:Code in the HTML.
• Internet Relay Chat: on (IRC) servers, Template:Code precedes the name of every channel that is available across an entire IRC network.
• In lightweight markup languages, such as wikitext, Template:Code is often used to introduce numbered list items.
• In the Perl programming language, Template:Code is used as a modifier to array syntax to return the index number of the last element in the array, e.g., an array's last element is at Template:Code. The number of elements in the array is Template:Code, 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., Template:Code, then Template:Code returns Template:Code. See the section on Array functions in the Perl language structure article.
• Template:Code is used in the Modula-2 and 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 Template:Char, being more intuitive than Template:Code or Template:Code. For example: Template:Nowrap
• In Rust, Template:Code is used for attributes such as in Template:Code.
• In OCaml, Template:Code is the operator used to call a method.
• In Common Lisp, Template:Code is a dispatching read macro character used to extend the S-expression syntax with short cuts and support for various data types (complex numbers, vectors and more).
• In Scheme, Template:Code is the prefix for certain syntax with special meaning.
• In Standard ML, Template:Code, when prefixed to a field name, becomes a projection function (function to access the field of a record or tuple); also, Template:Code prefixes a string literal to turn it into a character literal.
• In Mathematica syntax, Template:Code, when used as a variable, becomes a pure function (a placeholder that is mapped to any variable meeting the conditions).
• In LaTeX, Template:Code, when prefixing a number, references an arguments for a user defined command. For instance \newcommand{\code}[1]{\texttt{#1}}.
• In Javadoc, Template:Code is used with the Template:Code tag to introduce or separate a field, constructor, or method member from its containing class.
• In Redcode and some other dialects of assembly language, Template:Code is used to denote immediate mode addressing, e.g., Template:Code, which means "load accumulator A with the value 10" in MOS 6502 assembly language.
• in HTML, CSS, SVG, and other computing applications Template:Code is used to identify a color specified in hexadecimal format, e.g., Template:Code. This usage comes from X11 color specifications, which inherited it from early assembler dialects that used Template:Code to prefix hexadecimal constants, e.g.: ZX Spectrum Z80 assembly.
• In Be-Music Script, every command line starts with Template:Code. Lines starting with characters other than Template:Code are treated as comments.
• The use of the hash symbol in a hashtag is a phenomenon conceived by 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.
• In programming languages like PL/1 and Assembler used on IBM mainframe systems, as well as JCL (Job Control Language), the Template:Code (along with Template:Code and Template:Code) are used as additional letters in identifiers, labels and data set names.
• In J, Template:Code is the Tally or Count function, and similarly in Lua, Template: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 Template:Code over longer function names, this practice has become standard in the Lua community.
• In Dyalog APL, Template:Code is a reference to the root namespace while Template:Code is a reference to the current space's parent namespace.
• In Ada, the Template:Code character is used in based integer literals, which take the form Template:Code, where Template:Code is an integer from 2 to 16 specifying the radix, and Template:Code are the digits valid in that base (0-9, optionally A-F for bases above 10).

Other uses

• 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.
• Copy writing and copy editing: Technical writers in press releases often use three number signs, Template:Char directly above the boilerplate or underneath the body copy, indicating to media that there is no further copy to come.
• Footnote symbols (or endnote symbols): Due to its ready availability in many computer fonts and directly on computer keyboards, Template:Code and other symbols (such as the caret (Template:Code)) have in recent years begun to be occasionally used in catalogues and reports in place of more traditional symbols (esp. dagger, double-dagger, pilcrow).
• Linguistic phonology: Template:Char denotes a word boundary. For instance, Template:Code means that Template:Char becomes Template:Char 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.
• Medical prescription drug delimiter: In some countries, such as Norway or Poland, Template:Char is used as a delimiter between different drugs on medical prescriptions.
• Medical shorthand: The hash is often used to indicate a bone fracture. For example, Template:Code is often used for "fractured neck of femur". In radiotherapy, a full dose of radiation is divided into smaller doses or 'fractions'. These are given the shorthand Template:Char to denote either the number of treatments in a prescription (e.g. Template:Code), or the fraction number (Template:Code).
• As a proofreading mark, to indicate that a space should be inserted.
• Publishing: When submitting a science fiction manuscript for publication, a number sign on a line by itself (indented or centered) indicates a section break in the text.
• Scrabble: Putting a number sign after a word indicates that the word is found in the British word lists, but not the North American lists.
• Teletext and DVB subtitles (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. Template:Mono

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:

• Template:Unichar (Other attested names in Unicode are: Template:Sc.)
• Template:Unichar
• Template:Unichar
• Template:Unichar
• Template:Unichar
• Template:Unichar
• Template:Unichar
• Template:Unichar
• Template:Unichar
• Template:Unichar

Additionally, a Unicode named sequence Template:Resize is defined for the grapheme cluster Template:Code (#️⃣).Template:Efn

On keyboards

On the standard US keyboard layout, the Template:Char symbol is Template:Keypress. On standard UK and some other European keyboards, the same keystrokes produce the [[Pound sign|pound (sterling) sign, Template:Char symbol]], and Template:Keypress may be moved to a separate key above the right shift key.

See also

• Template:Unichar
• Template:Unichar
• Template:Unichar
• Template:Unichar2 ("looped square")
• Template:Unichar, the Chinese character for a well (Template:Zh-cjp)
• the game tic-tac-toe, which uses a similar grid pattern