The term 'coalfish' is a common name for two species of fish, the saithe (also known as pollock) and the coley. Both species are found in the North Atlantic and Arctic Oceans, and are important commercial fish species. The saithe is a long, slender fish with a silvery-green back and white underside, while the coley is a smaller, more rounded fish with a brownish-green back and white underside. Both species are popular for their mild flavor and firm texture.