Any one of many species of marine bivalve shells of the genus Mytilus, and related genera, of the family Mytidæ. The common mussel (Mytilus edulis; see Illust. under Byssus), and the larger, or horse, mussel (Modiola modiolus), inhabiting the shores both of Europe and America, are edible. The former is extensively used as food in Europe.
- Any of several marine bivalve mollusks, especially the edible members of the family Mytilidae and in particular Mytilus edulis, a blue-black species raised commercially in Europe. Mussels are often found attached to rocky surfaces or the sides of ships.
- Any of several freshwater bivalve mollusks of the genera Anodonta and Unio, found in the central United States, that burrow in the sand or mud of lakes and streams.