What does the # symbol mean on Twitter?

[Rock and Ride]

You know how they have the # symbol on Twitter and then an event/person/etc after it? What is it, and what do you do with it?

[Jeffrey]

It means a category. For example: #computer means that your tweet that contains this tag will go in the computer category.

[A_Sarcastic_Hell]

It means a HASH tag... which is like a keyword you are referencing...
Check this out... Twitter hash tags: http://hashtags.org/

They usually are short names for things... it is a way to tag your post to be associated in a group... when you search for them.

I use it all the time when talking about something like I am headed for a #run or I am at the SouthBySouthWest event #SXSW