what does eg: @username mean on twitter?

[Andy]

i use twiter some people update there twitter and it has the @symbol and a username then their update help please?

[Chelsea]

That means that tweet is directed to them. Lets say there's 2 people and their usernames are Paul and Bob. If Bob wanted to tell Paul to come over then he would tweet "@Paul can you come over later?"

And then unless you are following both Paul and Bob it will not show up on your main screen. Paul will receive the message.

It's kind of Twitter's way of writing on someone's wall on Facebook or commenting to someone in Myspace.