The haddock is a saltwater ray-finned fish from the family Gadidae, the true cods. It is the only species in the monotypic genus Melanogrammus. It is found in the North Atlantic Ocean and associated seas, where it is an important species for fisheries, especially in northern Europe, where it is marketed fresh, frozen and smoked; smoked varieties include the Finnan haddie and the Arbroath smokie. Other smoked versions include long boneless, the fileted side of larger haddock smoked in oak chips with the skin left on the fillet.

Cod is the common name for the demersal fish genus Gadus, belonging to the family Gadidae. Cod is also used as part of the common name for a number of other fish species, and one species that belongs to genus Gadus is commonly not called cod.