Twitter- What does it mean when people tweet and use the # sign before words?

[Krista]

People will tweet and then put #(insert comment) after their tweet. What does this mean?

I'm not fully aware of all the twitter rules.

[Qwerty]

it's called a hash tag. It's used to reference anything. It could be anything.

[Caitlin Jenkinson]

I think it means that your being kind of directed to what conversation / forum its on, or the key word fro that subject the conversation is based on. ummm...

[Dest]

Say if I tweeted something like "I hate eggs #thatisall" - The #thatisall would be highlighted. Clicking on it would lead to a search, where you can read other public "#thatisall" tweets.

It's a useful function for keeping track of topics. For example -
#adelaide - People living in Adelaide, Australia use it to keep track of events & talk to each other, without following each other.
#doctorwho - Whovians who watch the show, discuss what they like, or share something.

It goes on & on.