A universal joint is a joint or coupling connecting rigid shafts whose axes are inclined to each other. It is commonly used in shafts that transmit rotary motion. It consists of a pair of hinges located close together, oriented at 90° to each other, connected by a cross shaft. The universal joint is not a constant-velocity joint.

A constant-velocity joint is a mechanical coupling which allows the shafts to rotate freely and compensates for the angle between the two shafts, within a certain range, to maintain the same velocity.