What does the @ sign mean on Twitter?

[stargazengrle]

I see it all of the time, almost like it's a message/reference to someone but not a hash. How can I get it to go up on the person's Twitter wall, if that's even possible?

[Danielle]

its just something they put before someones user name like @daniellebock or whatever the persons user name is

[tonksloopy]

it's just so the messege could be sent to that person that has the "@" before their user name. if you type something..."hey @person how are you today?" they will automatically see it on their wall. you can mention as many people as you can.