A scallop is a kind of saltwater shellfish that swims by opening and closing its shell. Cooked scallops are a popular seafood as well.
The word scallop can actually refer to a few types of mollusks, including some clams and the thorny oyster. In the ocean, scallops are known for swimming extremely fast by moving their valves, or each half of the shell they live inside. You may also encounter scallops on the menu of a seafood restaurant. The curved edge of a scallop shell led to another meaning of scallop, "rounded ornamental edging," like the scallops on a skirt's hem or woodwork.