From Wikipedia: In common usage, the arm extends to the hand. It can be divided into the upper arm (sometimes called aftarm), which extends from the shoulder to the elbow, the forearm (also called antebrachium) which extends from the elbow to the hand, and the hand.
The humerus is one of the three long bones of the arm. It joins with the scapula at the shoulder joint and with the other long bones of the arm, the ulna and radius at the elbow joint. The elbow is a complex hinge joint between the end of the humerus and the ends of the radius and ulna.