The biceps is the large muscle on the front of your upper arm, between your shoulder and elbow. When you flex your arm to “make a muscle,” that bulge you see is your biceps contracting. The name comes from Latin words meaning “two heads” because the muscle attaches to your shoulder bone in two places.

Your biceps does important work every day: it helps you bend your elbow to lift things, pull open doors, or bring food to your mouth. When you do a pull-up or climb a rope in gym class, you're using your biceps to pull your body weight upward. The muscle works together with other arm muscles, but it's one of the most visible ones when your arm bends.

People sometimes use biceps as shorthand for physical strength generally, though your body has hundreds of other muscles doing equally important work. A person who's been lifting weights might be described as having “big biceps,” meaning their arm muscles have grown from the exercise.