gizzard, in many birds, the hind part of the stomach, especially modified for grinding food. Located between the saclike crop and the intestine, the gizzard has a thick muscular wall and may contain small stones, or gastroliths, that function in the mechanical breakdown of seeds and other foods. In this sense, the gizzard is comparable to the teeth of other animals. A few other animals, such as earthworms and some moss animals, also have gizzardlike structures.