If you are a Twitter user, the hashtag is your friend.
Hashtags are the # symbol, and on Twitter they are used to mark a certain subject for a search. For example, if I were to do this: #dance, it would categorize my tweet under dance in a search for that subject. While it doesn’t guarantee that people will find your tweets–it can really help!
Want to learn the details? Take a look at the Twitter page that gives you all the details.