What is gizzard?

The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including archosaurs, earthworms, some gastropods, some fish, and some crustaceans.

https://en.wikipedia.org/wiki/Gizzard

You may be familiar with the gizzard (the stomach of a bird) as one of the components of the giblets, sometimes found included in the interior of a whole bird purchased for cooking. The giblets (heart, liver and gizzard) may be cooked and served, or used as the basis for a giblet gravy. Birds are part of the group referred to above as archosaurs, which also includes crocodilians and a number of extinct animals.

https://en.wikipedia.org/wiki/Gizzard#In_cuisine