A Combat Team is often confused with a Fire Team and the names are often interchanged. The designation "Team" is used in reference to almost any small unit. A Combat Team (or a Section) is composed of two UNSC Marine Squads and numbers about 16-24 Marines, led by a Sergeant or Staff Sergeant. A Fire Team is smaller: 4-5 Marines.
The way to differentiate between the two is this: a Fire Team is part of a squad, whereas a squad is part of a Combat Team. By this logic, Fire Team Charlie and Fire Team Zulu were technically Combat Teams. A Fire Team would provide covering fire for the rest of the squad or an Assault Team to flank and destroy the enemy.