Frigates, destroyers, and modern cruiser roles

What is the difference between a frigate and a destroyer?

Historically and today the distinction is mainly one of role, with modern frigates commonly anti-submarine focused and destroyers commonly air-defence focused.

In the Second World War, a frigate developed as a more militarised corvette, between a corvette and a sloop, for anti-submarine warfare. A destroyer was a general-purpose escort and usually carried heavy torpedo armament. Modern destroyers commonly concentrate on air warfare, while frigates commonly concentrate on anti-submarine warfare. Missile numbers do not reliably distinguish them because national naming conventions vary: some navies call their large escorts frigates and others call them destroyers.