Please answer my Twitter question?

[Windowphobe]

It's a hashtag. Think of it as a manually-applied search keyword. For instance, one popular bit that's been going lately has been #1stdraftmovielines, in which people have been rewriting famous movie quotes to their presumed earlier, inferior versions. If you want to read a bunch of them, just search for that text string. (And if you want to write one of your own, add that to the message somewhere and it will be automatically included.)