Clams are shelled marine or freshwater molluscs belonging to the class Bivalvia. The term "clam" has no taxonomic significance in biology, but is often used to refer to any bivalve (a mollusc whose body is protected by two symmetrical shells) that is not an oyster, mussel, or a scallop, and that has a more-or-less oval shape. An exception is the razor clam, which has an elongate shell that suggests an old-fashioned straight razor.

Clams can be hard-shelled or soft-shelled, according to the degree of calcification of their shells. They are eaten raw, steamed, boiled, baked or fried. Clam chowder is a popular soup in which the primary ingredient is clam.

Examples of clams

• The hard clam or Northern Quahog: Mercenaria mercenaria
• The soft clam : Mya arenaria
• The surf clam : Spisula solidissima
• The ocean quahog : Arctica islandica
• The Pacific razor clam : Siliqua patula
• The giant clam: Tridacna gigas
• Asian or Asiatic clam : genus Corbicula