Team Slayer is the same game mode as Slayer, except the players are divided into teams. Team Slayer is also a social and ranked matchmaking playlist in Halo 3, and plays with the same rules and variants as Team Slayer.
In Custom Games, there are actually eight possible teams a player can be on, divided into colors: Red, Blue, Orange, Green, Brown, White, Grey, Purple. Other rules can also dictate the win conditions (by default, first to 50 kills for one team - this can be changed, as well as other variations such as making each player on a team get a minimum number of kills for the team to win).
Variations
Shotty Snipers
Players start out with a Sniper Rifle and a Shotgun. There are no weapons on map except Grenades.
Team Snipers
Players start out with a Sniper Rifle and a Magnum. There are no weapons on map except Grenades.
Team BRs
Players start out with a Battle Rifle and an Assault Rifle. Everything else is normal.
Team Rockets
Players start out with a Rocket Launcher. There are no weapons on map. This variation is only played in Social Slayer.