In the rating system of the Royal Navy used to categorise sailing warships, a second-rate was a ship of the line which by the start of the 18th century mounted 90 to 98 guns on three gun decks; earlier 17th-century second rates had fewer guns and were originally two-deckers or had only partially armed third gun decks. A "second rate" was the second largest class of warships in a hierarchical system of six "ratings" based on size and firepower.

They were essentially smaller and hence cheaper versions of the three-decker first rates. Like the first rates, they fought in the line of battle, but unlike the first rates, which were considered too valuable to risk in distant stations, the second rates often served also in major overseas stations as flagships. They had a reputation for poor handling and slow sailing. They were popular as flagships of admirals commanding the Windward and/or Leeward Islands station, which was usually a Rear-admiral of the red.