Frigate :

In naval terminology, a frigate is a warship, generally a relatively small one. The term has been used for warships of many sizes and roles, varying by era and country.

In the 18th century, the term referred to ships smaller and faster than a ship-of-the-line and used less for fighting fleet actions than for patrolling, escort, and, due to their ability to outrace many enemy ships, messenger duty.
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.

The age of sail :

The term "frigate" originated in the Mediterranean in the 15th century, referring to a galleass-type ship with oars, sails and a light armament.

By the 17th century, the phrase was used in England to describe a type of small, long, warship with small armament and a large crew used by Dunkirk Privateers for short-range raiding in the English Channel. The terms was soon adopted for any relatively fast and lightly built warships, the first in British service being the Constant Warwick of 1645.
Because the British navy required greater endurance than the Dunkirk frigates could provide, the term 'frigate' was soon applied less exclusively to any relatively fast and elegant ship. Even the mighty Sovereign of the Seas was described as 'a delicate frigate' after modifications to her in 1651.

The fleets built by the Commonwealth in the 1650s generally consisted of ships described as 'frigates', the largest of which were two-decker 'great frigates' of the third rate. Carrying 60 guns, these vessels were as big and capable as 'great ships' of the time; however, most other frigates at the time were used as 'cruisers'; independent fast ships. The term 'frigate' implied a long hull design, which in turn helped the development of the broadside tactic in naval warfare.
In French, the term 'frigate' became a verb, meaning 'to build long and low', and an adjective, adding further confusion.
According to the rating system of the Royal Navy, laid down in the 1660s, frigates were usually of the fifth rate, though small 28-gun frigates were classed as sixth rate.

The 'classic' frigate :

The 'classic' sailing frigate, well-known today for its role in the Napoleonic wars, can be traced back to French developments in the second quarter of the 18th century. The French-built Medee of 1740 is often regarded as the first example of this type. These ships were full rigged and carried all their main guns on a single gun deck, which had used to be the upper gun deck on similarly-sized two-decked ships earlier. The lower 'gun' deck now carried no armament and functioned as "berth deck" where the crew lived, and was in fact placed below the waterline of the new frigates. The new sailing frigates were able to fight with all their guns when the seas were so rough that comparable two-deckers had to close the gun-ports on their lower decks. Like the larger 74 which was developed at the same time, the new frigates sailed very well and were good fighting vessels due to a combination of long hulls and low upperworks compared to vessels of comparable size and firepower.

The Royal Navy captured a handful of the new French frigates during the early stages of the Seven Years' War (1756–1763) and were duly impressed by them, particularly for their inshore handling capabilities. They soon built copies and started to adapt the type to their own needs, setting the standard for other frigates as a superpower.
Royal Navy frigates of the late 18th century were based on the 1780-vintage Perseverance class, which displaced around 900 tons and carried 36 guns; this successful class was followed by the Tribune class batch of fifteen ships starting in 1801 that displaced over 1,000 tons and carried 38 guns.

In 1797, the US Navy's first major ships were 44-gun frigates (or "super-frigates"), which actually carried fifty-six to sixty 24-pounder long guns and 36-pounder or 48-pounder carronades on two decks, were exceptionally powerful and tough. These ships were so well-respected that they were often seen as equal to 4th-rate ships of the line, and RN fighting instructions ordered British frigates (usually of 38-guns or less) to never engage American frigates at any less than a 2:1 advantage. The USS Constitution, better known as "Old Ironsides", the oldest commissioned ship afloat, is the last remaining example of the American 44, if not the last sailing frigate.