A chin is part of a face. It's the part below the mouth, formed by the skin and flesh covering the front of the lower jaw. Only things with faces--that is to say, mostly, human beings, have "chins." A shark has jaws but no "chin." The jaws are two internal bones that hold the teeth and allow the mouth to bite. When you think of a "jaw" you are thinking of mostly of the biting function and the mouth. Because a chin is formed by flesh on top of the jaw, a chin can have a "dimple" or it can be "cleft." This is often thought to be handsome. The actor Kirk Douglas was famous for having a dimple on his chin. You can't have a dimple on a jaw, because the feature is formed in the muscles, not the bone. http://upload.wikimedia.org/wikipedia/commons/1/1f/Kirk_and_Michael_Douglas_-1969.jpg