The symbol # is most commonly known as the number sign, hash, or pound sign.

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The symbol # is most commonly known as the number sign, hash, or pound sign.

The symbol has historically been used for a wide range of purposes, including the designation of an ordinal number and as a ligaturedabbreviation for pounds avoirdupois (having been derived from the now-rare ℔).

Since 2007, widespread usage of the symbol to introduce metadata tags on social media platforms has led to them being known as "hashtags".

Indeed, the symbol alone is now frequently referred to as a hashtag itself.

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