The genus name Leucophaeus is from Ancient Greek leukos, "white", and phaios, "dusky". The specific atricilla is from Latin ater, "black", and cilla, "tail". Linnaeus appears to have misread his note atricapilla (black-haired), which would have been much more appropriate for this black-headed, but white-tailed, bird.
It breeds on the Atlantic coast of North America, the Caribbean, and northern South America. Northernmost populations migrate farther south in winter, and this species occurs as a rare vagrant to western Europe. The laughing gull's English name is derived from its raucous kee-agh call, which sounds like a high-pitched laugh "ha... ha... ha...".
Laughing gulls breed in coastal marshes and ponds in large colonies. The large nest, made largely from grasses, is constructed on the ground. The three or four greenish eggs are incubated for about three weeks
This species is easy to identify. It is 36–41 cm (14–16 in) long with a 98–110 cm (39–43 in) wingspan. The summer adult's body is white apart from the dark grey back and wings and black head. Its wings are much darker grey than all other gulls of similar size except the smaller Franklin's gull, and they have black tips without the white crescent shown by Franklin's. The beak is long and red. The black hood is mostly lost in winter.
Laughing gulls take three years to reach adult plumage. Immature birds are always darker than most similar-sized gulls other than Franklin's. First-year birds are grayer below and have paler heads than first-year Franklin's, and second-years can be distinguished by the wing pattern and structure.