 The genus name is from Ancient Greek "khelidonios", "swallow-like", from "khelidon", "swallow".The name 'white-winged tern' is the standard in most English-speaking countries; in the United Kingdom, this name is also the one used by the formal ornithological recording authorities, but the older alternative 'white-winged black tern' is still frequent in popular use.Adult birds in summer have short red legs and a short black bill (small and stubby, measuring 22–25 mm from the feathers, decidedly shorter than the head), a black neck (often with a pale gray back) and belly, very dark grey back, with a white rump and light grey (almost white) tail, which often looks 'square' in juveniles.