shad means: These delicate, small saltwater fish are closely related to herrings, alewife and sardines. These fish are bigger than herrings, and they spawn in freshwater. There are some species of shad that live on land and others in freshwater lakes. (in Cooking Dictionary)

What else does shad mean?

One of many marine fishes, chiefly from the genus. Alosa, Particularly A. sapidissima They swim up rivers in northern North American waters to spawn. Shad is closely related to herring. (in Merlin Dictionary)