The Rice University Neologisms Database

Literally meaning “away from keyboard,” this word expresses the state in which someone is temporarily no longer capable of participating in an online game. Coined by online computer game players who needed to inform others not physically present of their period of absence. This acronym message was typed out in place of the whole phrase to minimize time taken to communicate. If a person was away from a keyboard, he was unable to continue playing the online game for a duration. This literal meaning soon turned into a figure of speech in which the speaker was not necessarily far from the keyboard but just unable to continue playing for a duration. The relatively slow speed of typing is likely to have caused the formation of many similar acronyms. The word is somewhat of a jargon for video game players.