look up any word, like swoll:
 
1.
A unit of 30-40 soldiers, usually commanded by a lieutenant asisted by an NCO. A platoon is formed by at least two sections or squads (usually 3 or 4) and is smaller than a company. Typically, there are 3-4 platoons in a company. Most platoons are infantry platoons; some carry other designations such as mortar or heavy weapons platoons. A platoon is the smallest military unit led by a commissioned officer

Also a very kick ass movie from Oliver Stone that won Best Picture for 1986.
In the British Army, a platoon is led by a lieutenant or second lieutenant.
It's the same in the Canadian Forces and the U.S. Army.
by Adrian July 01, 2006