The Caspian tern is the world's largest species of tern, with a subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic of its genus, and has no accepted subspecies. The genus name is from Ancient Greek hudro-, "water-", and Latin progne, "swallow". The specific caspia is from Latin and, like the English name, refers to the Caspian Sea.
Hydroprogne caspia