In the military (at least the U.S. military), this is the smallest tactical unit into which a platoon may be divided. Commonly there are 4 squads to a platoon.

A Squad can consist of 8 to 12 men (or women) and is usually commanded by a Sergeant.

Squads also seem to encourage bonding between soldiers, especially in wartime. The size of a squad is small enough for the members to know each other well (critical in combat) but still large enough to pose a threat. This can also be seen as a drawback, though, since the death of a comrade weighs heavy on the morale of a unit.