Thalasseus, the crested terns, is a genus of six species of seabirds in the tern family. These large terns breed in very dense colonies on coasts and islands, and exceptionally inland on suitable large freshwater lakes close to the coast. They feed by plunge-diving for fish, almost invariably from the sea. These species have long thin sharp bills, usually a shade of yellow or orange except in the Sandwich Tern where the bill is black with a yellow tip in most subspecies.
All species have a shaggy crest. In winter, the foreheads become white.