See abdomen. The underside of the body of certain vertebrate animals, such as a snake. A cut of meat from the underside of an animal, especially a pig. Informal The stomach. An appetite for food. The womb; the uterus. A part that bulges or protrudes: the belly of a sail. Anatomy The bulging, central part of a muscle. A deep or central interior space: the engine in the belly of a ship; fish down in the belly of a river.