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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 US Cavalry and the King's Troop Royal Horse Artillery where a troop is a subunit comparable to an infantry company or artillery battery. Historically the remainder of the Royal Horse Artillery used the term troop in the same manner but they eventually aligned with the rest of the Royal Regiment of Artillery in referring to troops as subordinate to artillery batteries.

Troops is often used to refer to the other members of one's company or cause, but because of its military connotations, it conveys a particularly altruistic type of dedicated worker. Traditionally, troops refers to the soldiers in a military.

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).