GKP (Gold Kill Points?) is a way for groups (Usually PUGs) to decide who gets loot that drops in an instance. Rather than using DKP, when an item drops, players bid gold for the item, and the person who bids the most wins. At the end of the entire raid (Or each boss, as some GKP leaders tend to do) the gold is then split among all the players attending the GKP run.
GKP runs can often have the same problems that PUGs have, such as incompetent players. They can also suffer from a dishonest raid leader who doesn't split the gold at the end of the run, and instead keeps it for themself.