Squad
From Halopedia, the Halo wiki
A squad is a order of battle in the UNSC military, most specifically the UNSC Marine Corps. It is composed of two fireteams, each comprised of 2-5 men. Fireteams who are organized into a squad are usually in numbers of 4-5. The squad is often commanded by either a staff sergeant or corporal. Squads within a platoon are numbered i.e. First Squad, Second Squad, and so forth. Squads comprise the the smallest unit in a UNSC formation capable of performing most tasks, such as storming a enemy-held building, or engaging in combat. The squad, as stated eariler, is futher divided into fireteams, who coordinate very closley with one another to improve sqaud member-to-squad member communication. Most times in a Halo Single Player situation, The Player will lead squads of Marines into battle on various missions.