A ball-and-socket joint is formed by the ball-shaped end of one bone fitting into the hollowin another. It allows movement backward or forward, movement sideways, and rotation..
A ball-and-socket joint is a type of synovial joint that allows one part to rotate at almost any angle with respect to another. Ball-and-socket joints occur naturally, as in the human hip and shoulder joints, and are also used in machinery. Of all synovial or diarthrodial (fully moveable) joints in the body, ball-and-socket joints are the most mobile and allow movement in three planes.