any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes; "a diet high in protein"
a book of blank pages with pockets or envelopes; for organizing photographs or stamp collections etc
one or more recordings issued together; originally released on 12-inch phonograph records (usually with attractive record covers) and later on cassette audio tape and compact disc