In Modern Warfare 2, a person or group of people who use Tactical Insertions to their advantage, go to a rarely-used place on a map, set the insertions, then continuously kill each other to get a free nuke or a bunch of free headshots. This is considered complete and utter cheating and is commonly rejected by professional players. MW2 pro "Sandy Ravage" has a series on YouTube called Booster Justice which is him killing boosters to no end.
Yo, want to boost?" "No, I don't cheat, you booster.