Definition of mussels:
(n) :
Any of several groups of bivalve shellfish with elongated, asymmetrical shells.
(n) :
A saltwater mussel, usually edible, of the order Mytilida in subclass Pteriomorphia.
(n) :
A freshwater mussel, usually edible, of the order Unionida in subclass Palaeoheterodonta.
(n) :
Any of certain other bivalves of somewhat similar appearance, such as the zebra mussel and quagga mussel of the family Dreissenidae in subclass Heterodonta.