An auk or alcid is a bird of the family Alcidae in the order Charadriiformes. The alcid family includes the murres, guillemots, auklets, puffins, and murrelets. The word "auk" is derived from Icelandic álka, from Old Norse alka (auk), from Proto-Germanic *alkǭ (sea-bird, auk).
Apart from the extinct great auk, all auks can fly, and are excellent swimmers (appearing to "fly") and divers, but their walking appears clumsy.
Several species have different English names in Europe and North America. The two species known as murres in North America are called guillemots in Europe, and the species called little auk in Europe is referred to as dovekie in North America.