A troop is a military unit, originally a small force of cavalry, subordinate to a squadron. In many armies a troop is the equivalent unit to the infantry section or platoon. Exceptions are the Royal Horse Artillery and the US Cavalry, where troop refers to an infantry company or artillery battery.A cavalry soldier of private rank is called a trooper in many Commonwealth armies (abbreviated Tpr, not to be confused with trouper).A related sense of the term troop refers to members of the military collectively, as in the troops; see Troop (disambiguation).