Gamers lingo, almost always refering to FPS (first person shooter) games. Killwhore can have several meanings, all derogatory:

1. A term used by a player who is sick of dieing to one player.

2. A hateful word used towards people who play the game the way it was ment to be played and playing well.

3. Somone who defies direct orders the commander / team leader just so he or she can scrape up a kill or two before they die.