A gizzard is an internal organ that some kinds of animals have in their digestive tracts. Turkeys and chickens use their gizzard to grind up food, often along with small stones they swallow.
Some crustaceans and fish have gizzards, and so do birds, crocodiles, and alligators. Dinosaurs had gizzards too! If you've ever cooked a Thanksgiving turkey, you might recognize the gizzard as one of the parts that are removed before roasting, but in many cuisines the gizzard is a delicious treat. In a live animal, the gizzard performs the function of teeth, grinding food to make it more digestible.