It's called idle. It's not an away message, it just dims your name. I don't allow people to see if I'm idle or not because I don't want them to know whether or not I'm ignoring them or just not there.
You're such a newb. I don't have to prove to you that I don't spend every waking moment on the internet just like you don't have to prove to us that you don't stick things up your ass. We're all pretty sure you do though.