A frigate is a warship. The term has been used for warships of many sizes and roles across eras.
In the 18th century, the term referred to ships which were as long as a ship-of-the-line and which carried a full rig of sail on three masts, but were faster and with lighter armament, used for patrolling and escort. In the 19th century, the armoured frigate was a type of ironclad warship and for a time was the most powerful type of vessel afloat.
In modern navies, frigates are used to protect other warships and merchant-marine ships, especially as anti-submarine warfare (ASW) combatants for amphibious expeditionary forces, underway replenishment groups, and merchant convoys. But ship classes dubbed "frigates" have also more closely resembled corvettes, destroyers, cruisers and even battleships.