A scallop is a common name primarily applied to numerous species of saltwater clams or marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families within the superfamily Pectinoidea, including the thorny oysters.

Scallops are a cosmopolitan family of bivalves found in all of the world's oceans, although never in freshwater. They are one of the very few groups of bivalves to be primarily "free-living," with many species capable of rapidly swimming short distances and even migrating some distance across the ocean floor.

Many species of scallops are highly prized as a food source, and some are farmed as aquaculture. The word "scallop" is also applied to the meat of these bivalves, the adductor muscle, sold as seafood. The brightly colored, symmetric, fan-shaped scallops shells with their radiating and often fluted ornamentation are valued by shell collectors. They have been used since ancient times as motifs in art, architecture, and design.
 

Shellfish

Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of mollusks, crustaceans, and echinoderms. 

Although most kinds of shellfish are harvested from saltwater environments, some are found in freshwater. Shellfish are among the most common food allergens.