a.k.a. pound sign, hash key, hashtag, number sign, square key, gate, hex sign, net
The pound symbol (also known as the "hash" symbol) is most commonly used to represent numbers, as in, "I'll answer #3." In some versions of Unix, it is the system prompt. It has a variety of uses online, either as part of a cryptic password, or in creative renditions of ASCII art, or smileys.
The hashtag went mainstream when Twitter users began adding it to a word or phrase like #word when searching for tweets. For example, @netlingo often tweets under the hashtage: #acronymoftheday. It also means "net."
NetLingo Classification: Symbols