Shellfish is a culinary term for aquatic invertebrates used as food: molluscs, crustaceans, and echinoderms. Both saltwater and freshwater invertebrates are considered shellfish. Shellfish is a misnomer, because these invertebrates are definitely not fishes. The term finfish is sometimes used to distinguish ordinary (vertebrate); fish from shellfish.

Molluscs commonly used as food include the clam, mussel, oyster, eye winkles, and scallop.

Some crustaceans commonly eaten are the shrimp, prawn, lobster, crayfish, and crab.

Echinoderms are not eaten as commonly as mollusks and crustaceans. In Asia, sea cucumber and sea urchins are eaten.

Edible cephalopods, such as squid, octopus, and cuttlefish and terrestrial snails, though all molluscs, are sometimes classified as shellfish and sometimes not.