Afk

"AFK" is short for "away from keyboard," meaning that a player is not actively playing the game.

From "help afk:"

Afk:

Afk allows you to tell other players that you are away from the keyboard
and are unavailable right now. Typing anything after you return from AFK will
take you out of AFK mode and attempt to do that command (for example, typing
'score' after you return from being AFK will attempt the command 'score'). 
While in AFK mode, all players that send you tells or use socials on you will
see that you are AFK, so they'll know you aren't currently at your keyboard.