Classic
cheat code from the
ID software game
Doom. Typing it gives the player all
keys,
weapons and full
ammo.
There are several proposed meanings for KFA, such as "Keys Full Ammo" or "Kick Fucking Ass". Personally I doubt any suggestion that does not interpret the K as "Key", since the code
idfa has the same effect, except that it does not give the player the keys.
The code has the same effect in Doom II. Using it in the follow-up game Heretic gives the response "cheater - you don't deserve weapons" and disarms the player. If you really want to cheat in Heretic you should use "rambo" instead.