Your chin is the somewhat pointy part of your jaw at the bottom of your face, below your mouth. When a man has a bushy beard, it usually covers his cheeks and his chin.
Humans are unique in having a chin — it's thought to have evolved in part from our habit of using speech. When chin is a verb, it means to do a pull up on an exercise bar, lifting your full weight until your chin touches the bar. In the late 16th century, to chin meant to affectionately rub chins with someone else, and in 1880s American slang, it also meant "to gossip."