A jaw refers to the bones in your face that hold your teeth and allow you to open and close your mouth. You have two jaws: the upper jaw (which is fixed and doesn't move) and the lower jaw (which moves up and down when you talk, chew, or yawn). When you bite into an apple or grind your teeth, you're using the powerful muscles attached to your jaw.

Animals have jaws too, and they vary wildly depending on what the animal eats. A great white shark has rows of razor-sharp teeth in massive jaws that can bite with incredible force. A deer has a gentle jaw designed for chewing plants. Scientists study fossilized jaws to learn what extinct creatures ate and how they lived.

When someone's jaw drops, it means they're so surprised that their mouth falls open without them meaning to. If someone tells you to pick your jaw up off the floor, they're teasing you about looking shocked. People also use jaw as a verb meaning to talk at length, especially in an argumentative way: two people might jaw back and forth about which superhero is strongest.