A troop is a military sub-subunit, originally a small formation of cavalry, subordinate to a squadron. In many armies a troop is the equivalent element to the infantry section or platoon. Exceptions are the Royal Horse Artillery and the US Cavalry, where troops are subunits that compare 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 "troops" refers to members of the military collectively, as in "the troops"; see Troop (disambiguation).