Comment by nandhp

> In the world outside of Twitter, though, it is still “the number sign.”

Or, increasingly commonly, "hashtag":

"What is the use of the hashtag(#) on a telephone?" https://answers.yahoo.com/question/index?qid=20130329025332A...

"How to play C hashtag minor" http://i.stack.imgur.com/S4pcU.jpg (via http://ux.stackexchange.com/questions/62190/)