Squad

Squads are the second smallest infantry units in the UNSC Army and Marine Corps. Squads are typically led by non-commissioned officers and don't contain any commissioned officers. A squad is roughly equivalent to a Spartan-IV Regiment section or a Covenant Army lance. A fireteam is immediately below a squad, while a platoon is immediately above.

More information at: halopedia and wikipedia.

Background
Squads are made up of nine or thirteen to sixteen men and led by an NCO. A squad's organisation may vary between squads, but is generally the same throughout the UNSC Army and Marine Corps. Squads are usaully made up of two or three fireteams.

Structure
Typically, a squad will contain a squad leader and three fireteams of four or five men. The squad leader will usually by a staff sergeant (Army) or a sergeant (Marines) and wield an MA37 ICWS (Army) or an MA5B ICWS (Marines). The fireteams are usaully commanded by corporals and contain three or four other members of a lower rank. Three squads make up one platoon. In the army, squads are made up of two fireteams, while they are made up of three in the marines.