In naval warfare, an ocean escort is a term that encompasses a wide range of economical warships that can provide, in "blue water", protection to a convoy of commercial ships. They are most capable in anti-submarine warfare, have some capability for anti-air warfare, and, in the time when anti-surface warfare primarily used guns, had minimal capability against a plausible convoy raider.
A ship of this class may well be built to commercial, rather than warship, standards of survivability and speed. Any plausible escort will be as fast or faster than any transport in a convoy, which is adequate for the situation. In some cases, they have been originally built as a warship, but no longer capable for fleet action, such as an older destroyer, or, when there was a threat from heavily gunned raiders, perhaps an older cruiser or battleship.
Terms used for such vessels, when not a warship design, included destroyer escort, sloop, and frigate. The terms corvette and submarine chaser were sometimes used, but historically these were coastal, not blue-water escorts. Corvette, however, is becoming associated with more powerful warships.
After the Second World War, the United States went through a decade or two of redefining terms, so that "frigate" referred to a large destroyer, which for a time was called a "destroyer leader", and actually had the characteristics of a light cruiser.
In the Royal Navy and U.S. Navy, respectively, the Type 23-class and Oliver Hazard Perry-class frigates have come back to a modest standard of ocean escort. The British ship is generally more capable, retaining anti-shipping missiles and modest area surface-to-air missiles that the Perrys no longer carry. Both types, however, would have been utterly fearsome anti-submarine warfare platforms in WWII, and still are credible in many situations. They also carry helicopters, which both increase their antisubmarine reach, and can attack surface vessels, especially fast attack craft or small pirate vessels apt to be found in narrow waterways.