Why do people put # Then something after that?

[BILL]

What the hell does that mean?

[Aubrey]

Something to do with twitter.

[JohnAdriaan]

What you're describing is called a "hashtag". The Twitter system uses these to group all Tweets with the same hashtags, so that others interested in the same topic can see all of the same kind of Tweets.

Anyone can make one up: they only become popular when lots of people use the same one, and sometimes there can be some funny collisions, where people use a hashtag for something that has already been used for something completely different.

And since so many people use or at least read Twitter, the hashtag has become common outside of just Twitter.

[xdazzlingdiamonds]

it's a hashtag. twitter started it.

for example:
#DamnThisQuoteIsTrue
#KimKardashianDivorce
#theawkwardmomentwhen

they're like 'top trending' things people are talking about.