n (obsolete) Primarily, a square; hence, a square body of troops; a body of troops drawn up in a square.
n (military|army) A body of cavalry comprising two companies or troops, and averaging from one hundred and twenty to two hundred soldiers.
n (military|navy) A detachment of vessels employed on any particular service or station, under the command of the senior officer; as, the North Atlantic Squadron.
n (military|air force) A tactical air force unit; consists of at least two flights; multiple squadrons make up a group.