What dise AFK mean?

AFK stands for 'Away From Keyboard'. The meaning is self-explanatory: if you leave your computer or console without disconnecting from the game, you are AFK.

Usually a player who does nothing in an online game for long periods of time is either AFK or in some kind of UI (such as a chat box).
AKF is also referred to AFK, often mispelled.

It is an internet slang, which means 'Away From Keyboard'.
It's short for "away from keyboard" when your sending a text examples:brb,ttyl, and g2g, or gr8