What does it mean when people use the pound sign (#) on the Internet?

[Chrsitian]

Sometimes people on Facebook will put a status, and on the end of the status they put the pound sign: #

Example: some chick's status said
"we broke up today.

#stupid mistakes"

[BILL]

Its used in twitter..... ITs called a hashtag

[Paige]

It's a hashtag that originated from twitter. Used to shows thoughts, feelings or emotions. Some have tried to use it on Facebook, but it only belongs on twitter.

[1234]

It started on teitter, i guess people are carrying it over to facebook. But it's called hashtagging. It's kind of a way to say like why or the topic or a little extra information.

[TheJakeonaut]

The # is commonly used on twitter to categorize (referred to as a hashtag) the subject of a post. It helps track trending topics and to make searching easier, but is sometimes used as a joke or at the posters discretion.

Some people may have their Facebook and Twitter linked so the formatting wouldn't make sense on other sites.