What does # before a word mean in Twitter?

[twilight]

I've seen people tweet things like #classy and #eric. . . what does that mean??

[Kristina]

word is a way of tagging or tracking, it's called a hashtag and can identify posts. Check out more at: hashtags.org, that should get you on the right track.

[Boboo]

Words with the # (= a hash) in front of it are called hashtags. They are used in twitter to identify topics.
For instance, if you want to find all the tweets that are about the olympics, you search for #olympics
If you tweet about the olympics, you put #olympics in your tweet.