Any of various lightly built seabirds in the gull family Laridae, order Charadriiformes, with pointed wings and bill, and usually a forked tail. Terns plunge-dive after aquatic prey. They are 20–50 cm/8–20 in long, and usually coloured in combinations of white and black. They are extensively distributed, especially in temperate climates.

Species
The common tern Sterna hirundo has white underparts, grey upper wings, and a black crown on its head. The Arctic tern Sterna paradisea migrates from northern parts of Greenland, North America, and Europe to the Antarctic, thereby ensuring most of its life is spent in daylight. The Antarctic tern Sterna vittata has a striking blood-red beak; it does not migrate.

A number of species occur in Britain, in addition to the common and Arctic terns. They are the Sandwich tern S. sandvicensis, the little tern S. albifrons, and the roseate tern S. dougallii.

The black tern and other similar species known as marsh terns are placed in the genus Chlidonias. They are distinguished by their shorter bills, short and slightly forked tails, and less fully webbed feet.