From Halopedia, the Halo wiki
Multi-Team is a multiplayer playlist in Halo 2, Halo 3, Halo: Reach, Halo 4 and Halo 5: Guardians  It pits multiple small teams against each other in slayer and objective based games. Halo 2 used four teams of three, Halo 3 used four teams of two, and Halo: Reach used four teams of three. It is unranked and guests may join.
Prior to the update on February 8, 2011, Multi-Team used six teams of two. After the update, it was changed to four teams of three. Rocket Race was replaced with Rocket Hog Race, and 3 Ball was added.
Team Size: 3