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The correct backwardly compatible HTML Escape sequence for a number sign
(ASCII - ISO 8859-1 Latin-1)

The mesh operator, part of the Intercal character set.

the # stands for "channel" on IRC, is used as a comment tag in many programming languages and as a "number"-sign.

For example:
#everything on IRC
# this is a comment in my source code
or simply #5 (Number five)
Where I come it's pronounced 'th'. The connection to numeral order is obvious, but I don't know which one came from which.

  • In CPP, '#' is the prefix for preprocessor (as if there were the other sort) commands.
  • In CPP as GNU extension, inside macros '##' works as an escape that evaluted into a null, with an addition: if used before a "rest" parameter that is empty, it will remove the preceding commas.

    #define foo(a,b...) bar(a,##b)

    evaluates into


  • Wall character in ADOM.
  • Prefix for extended commands in NetHack.
  • Comment tag in most text-type configuration files too.
  • One of the classic text separators.
  • Also known as pound and risuaita.
  • Mostly really useless character, which is why it's so damned hard to think of more entries for this list
This is the pound sign. It came about from old english measurements, though the weight pound is now abbreviated lb instead of #. Most phones have a key with this character, and along with 10 numerals and the asterisk (* or 'star') it makes up the standard 12 key phone keypad, devloped by AT&T for their new touch-tone keypad. Touch Tones, incidently, support 16 keys, the other four are labelled A, B, C and D, and are not normally used.

It, #, is also used in musical notation to idicate that a note should be sharp. The musical scale includes 12 notes. Some combinations of notes are not in harmony with each other, so typically you use only 7 of the twelve in a given piece of music. To keep things simple, they only named 7 notes (ABCDEFG), and placed the other five inbetween the seven. The # sign is used to show that the note above the current note is to be used, so an F# would actually use one of the 'extra' five notes that lies between F and G. A flat is the opposite (ie, a G flat is the same as an F sharp)

In American english it is most often pronounced 'Pound' in relation to phone and keyboard buttons, and sharp in relation to music..

Also pronounced hash (my personal pronunciation), octothorpe if you want to confuse people, or sha, as in shabang (#!), and AFAIK only when used there. Brits don't pronounce it 'pound', because then we'd mix it up with the UK pound symbol, '£'.

...and of course there is the ever-popular pigpen/pig-fence moniker as well. These terms get extra points in my book on the basis that they are more fun. (Not to mention that they are also the closest approximation to a physical description.)

The # sign (approximated), also known as the sharp can appear amid a song (an accidental), or in the key signature. Any note that falls on the note modified by the sharp will cause any previous accidental or key signature (for that note) to be considered moot and the new, sharped, value to take its place. The value is then raised a half-step harmonically.

For example:

  • C becomes C# (which is enharmonically the same as a Db).
  • Db becomes a D# (which is the same as Eb)
  • E becomes E# (which is the same as F)

And so on.

A # drawn anywhere can also be used as the playing field for the popular ultra-portable game of tic-tac-toe, in which two players take turns battling it out with x's and o's to see who can get three in a row.

See tic-tac-toe for a painfully in-depth description of the game, including strategies.

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