Your jaw is the bottom, hinged part of your skull that holds your teeth. When you have a cavity, it can make your whole jaw hurt.
In humans, our jaw is the bony part of the head that contains our mouth and teeth. All animals with spines have jaws. Besides this anatomical meaning, you can use jaw as a verb to mean "chat." You might love to get together with your friends and jaw about unimportant things. You can also say "My jaw dropped" to mean "I was shocked or amazed." Jaw comes from the Old French joue, which means "cheek or jaw."