The term used to describe a boneless, lean cut of meat, fish or poultry. Fillet of beef is a prime cut and different parts of it are called different names depending on which part of the fillet they're cut from, including filet mignon, tournedos and châteaubriand. You also 'fillet' a fish to remove the bones. You can find out more about beef in our Cook's Guide. You can find out more about filleting fish in our Cook's Guide.