A name given to various species of arctic sea birds of the family Alcidæ. The great auk, now extinct, is Alca (or Plautus) impennis. The razor-billed auk is A. torda. See Puffin, Guillemot, and Murre.
- Any of several diving sea birds (family Alcidae) of northern regions, such as the razor-billed auk, having a chunky body, short wings, and webbed feet.