Number sign is the Unicode preferred name for the glyph or symbol #.

It is so used in the United States and Canada, where No. would be used in the United Kingdom (and also Canada since the influence comes from both directions).

The number sign's Unicode value is 0023 in hexadecimal and its ASCII value is 23 in hexadecimal.

It has many other names (and uses) in English. (Those in bold are listed as alternative names in the Unicode documentation.)

  • comment sign
  • crosshatch
    • resemblance
  • crunch
    • ?
  • fence, gate, grid, gridlet
    • resemblance
  • hash / hash mark / hash sign
    • common name outside the US, particularly in the UK
    • Used in the UK on touch-tone telephones – "Please press the hash key!"
  • pound / pound sign
    • Used as the symbol for the pound avoirdupois in the U.S. (where lb. would be used in the UK and Canada). Never called 'pound' in the UK.
      • 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 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."
    • Used in the U.S. and Canada on touch-tone telephones – "Please press the pound key!"
  • hex
    • from its use to denote hexadecimal values in some markup and programming languages; e.g., HTML
  • octothorn
    • William Sherk in 500 Years of New Words (1983), p. 272, has the following entry: "Octothorn, The number sign (#); so called because there are eight points, or thorns, sticking out of it ... ."
  • octalthorpe / octothorp / octothorpe
    • disputed origin: maybe
      • (i) thought to look like a group of eight fields surrounding a village (Norwegian thorpe) [¿and ostensibly used in cartography?]; or
      • (ii) octo- for its eight points, plus the surname Thorpe – see Weird Words entry [1] (but see the World Heritage Dictionary entry [1]); or
      • (iii) The Pasadena Star-News reported October 20, 1981, p. A-3, "According to the folks at Bell Laboratories in New Jersey, a rumor started in the 1960's or earlier ... that this symbol is called an octothorpe. One story has it that the rumor was started ... by one Charles B. Octothorpe." In another Star-News article on November 3, 1982, p. B-4, the word is written without the final e and refers to John B. Octothorp.
  • pig pen
    • resemblance
  • sharp
  • square
    • often misattributed as the UK name for #, in reference to touch-tone telephones. It has never been known as 'square'. From the earliest days of # appearing on telephones, it has been called 'hash'. (However, in French the # key on a telephone is called le carré.)
  • tic-tac-toe (US) / noughts-and-crosses (UK)
    • resemblance to game board
  • widget mark
    • ?

The pronunciation of # as `pound' is common in the US which can cause confusion. The British Commonwealth has its own, rather more apposite, use of `pound sign. On British keyboards the UK pound currency symbol often replaces #, with # being elsewhere on the keyboard. The US usage derives from an old-fashioned commercial practice of using a # suffix to tag pound weights on bills of lading. The character is usually pronounced `hash' outside the US. There are more culture wars over the correct pronunciation of this character than any other, which has led to the ha ha only serious suggestion that it be pronounced `shibboleth' (see Judges 12:6 in an Old Testament or Tanakh).

In Hebrew, called:

  • sulamit (from sulam == 'ladder' + -it, feminine ending)

In Portugal, called:
  • cardinal

References (as numbered above)

  1. World Heritage Dictionary
  2. Weird Words