What do you call the symbol #?
I would call it a hash or hashtag, but quite a few other names are available, including number, number sign, number mark, pound sign, hash sign, hash mark, crosshatch, crunch, fence, flash, garden fence, garden gate, gate, grid, hak, hex, mesh, octothorp, oof, pig-pen, punch mark, rake, scratch, scratch mark, tic-tac-toe and unequal.
It is thought that it comes from the symbol ℔, a ligature of l and b which stands for the Latin libra pondo (pound weight). Over time it became simplified until it morphed into #. The image is a stylized version of this symbol [source].
# is described as “number” in a treatise on bookkeeping from 1853. It was included the Remington Standard typewriter keyboard from about 1886, and was used in teleprinter codes. In 1968 it was included on touch-tone telephone keypads, and started to be used more extensively in the early 1980s. It was used to label groups and topics on internet relay chat (IRC) from about 1988. This lead Chris Messina, an American blogger and consultant, to propose its use to tag topics on Twitter in 2007. He became known as the inventor of the hashtag [source].
The name octothorp, which was apparently invented at Bell Telephone Laboratories in 1968. Variants include octothorpe, octathorp and octatherp. The name combines octo- (eight) from Latin, with the English thorp (hamlet, village), as it looks like a village surrounded by eight fields. Other stories about the origins of this name are available.
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