5 definitions of AFK. Definition of AFK in Slang/Internet Slang. What does AFK stand for?. AFK is commonly used with a descriptor like " afk bio" (you are going to the washroom), or " afk phone" (you are answering a phone call). AFK is. It could also mean that a person isn't logged in at a particular place (he/she could then be refered to as AFK eventough it's possible he/she is just playing.