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Number sign is a name for the symbol #, which is used for a variety of purposes, including (mainly in Canada and the United States) the designation of a number (for example, "#1" stands for "number one"). In recent years, it has been used for "hashtagging" on social media websites. The term number sign is most commonly used when the symbol is used before a number. In the United States and Canada, it is sometimes known as the pound sign (particularly in the context of its use on telephone keypads), and has been traditionally used in the food industry as an abbreviation for pounds avoirdupois. Outside of North America the symbol is called hash and the corresponding telephone key is called the "hash key", and the term "pound sign" usually describes the British currency symbol "£". The symbol is defined in Unicode as . The symbol may be confused with the musical symbol called ''sharp'' (). In both symbols, there are two pairs of parallel lines. The main difference is that the number sign has two horizontal strokes while the sharp sign has two slanted parallel lines which must rise from left to right, in order to avoid being obscured by the horizontal musical staff lines. Although the signs are strictly speaking different, one of the names for the telephone number sign key in French is ''dièse'' (sharp sign). ==Origin== It is often claimed that the use of the number sign for pound derives from a series of abbreviations for pound, the unit of weight. According to this suggestion, the symbol goes back to the abbreviation ''lb.'' for "pound" (Roman term ''libra pondo'' or "pound weight");〔"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." Keith Gordon Irwin, in ''The Romance of Writing'', p. 125 The Unicode character is intended to represent this ligature.〕〔 this abbreviation was printed with a dedicated ligature type, with a horizontal line across, so that the lowercase letter "l" would not be mistaken for the numeral "1". Ultimately, the symbol was reduced for clarity as an overlay of two horizontal strokes "=" across two forward-slash-like strokes "//". Alternative theories suggest that the name "pound sign" is a result of the fact that character encodings have historically used the same code for both the number sign and the British pound sign "£". Claims have included ISO 646-GB as well as the Baudot code in the late 19th century,〔(【引用サイトリンク】url=http://languagelog.ldc.upenn.edu/nll/?p=2461 )〕 however its usage as a pound sign predates all of these code sets. Examples of this usage exist at least as far back as 1850,〔(【引用サイトリンク】url=http://widespacer.blogspot.com/2015/10/the-sign-of-number.html )〕 and its double meaning is described in a book-keeping text from 1880. Number sign usage dates back to at least 1853. The symbol appears to be used primarily in written form, while in the printing business, the numero (№) symbol and barred-lb (℔) are used for "number" and "pounds" respectively. It appeared on typewriter keyboards as early as 1886, but was not used on the keyboards used for typesetting.〔 "Hash sign" is found in South Africans writings from the late 1960s,〔''Research Review. Navorsingsoorsig'' vols. 18-21, pp. 117, 259 (1968)〕 and from other non-North-American sources in the 1970s. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Number sign」の詳細全文を読む スポンサード リンク
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