What does AFK mean?
AFK is an acronym for "away from keyboard".
It's commonly used in multiplayer games and chat rooms to let other players know that you will be unavailable for a short time (away from keyboard), or to quickly explain an idle period.
Well, I'm away from my keyboard right now.
I'll tell you when I get back.
AFK simply means Away From Keyboard. It's commonly used in chatrooms and online games and it basically means that you won't be available (Not at the keyboard = Not in front of your computer).
Just in case you're wondering what RE or WB means: You'll see these two abbreviations quite often in onlinegames together with AFK. Re which basically means Returned and WB which stands for Welcome Back.