A frigate () is a type of warship. In different eras, ships classified as frigates have had very varied roles and capabilities.
In the 17th century, a frigate was any warship built for speed and maneuverability, the description often used being "frigate-built". These could be warships carrying their principal batteries of carriage-mounted guns on a single deck or on two decks (with further smaller carriage-mounted guns usually carried on the forecastle and quarterdeck of the vessel). The term was generally used for ships too small to stand in the line of battle, although early line-of-battle ships were frequently referred to as frigates when they were built for speed.
In the 18th century, frigates were full-rigged ships, that is square-rigged on all three masts, they were built for speed and handiness, had a lighter armament than a ship of the line, and were used for patrolling and escort. In the definition adopted by the British Admiralty, they were rated ships of at least 28 guns, carrying their principal armaments upon a single continuous deck – the upper deck – while ships of the line possessed two or more continuous decks bearing batteries of guns.
In the late 19th century (beginning about 1858 with the construction of prototypes by the British and French navies), the armoured frigate was a type of ironclad warship that for a time was the most powerful type of vessel afloat. These were still described as "frigates" because such ships still mounted their principal armaments on a single continuous upper deck, in the manner of older sailing frigates. However, by the end of the 19th century, developments in ironclad warships had made this type of ship obsolete and the term "frigate" became obsolete.
During the Second World War the name 'frigate' was reintroduced to describe a seagoing escort ship intermediate in size between a corvette and a destroyer. After World War II, a wide variety of ships have been classified as frigates. Often there has been little consistency in usage. While some navies have regarded frigates as principally large ocean-going anti-submarine warfare (ASW) combatants, others have used the term to describe ships that are otherwise recognisable as corvettes, destroyers, and even nuclear-powered guided missile cruisers. Some European navies use the term "frigate" for both their destroyers and frigates. The rank "frigate captain" derives from the name of this type of ship.