A universal joint, often called a U-joint, is a mechanical device that allows for the transmission of rotary motion between two shafts that are not in a straight line. It consists of two yokes connected by a cross-shaped component, enabling flexibility in movement. This design helps accommodate misalignment and varying angles between the shafts. Universal joints are commonly used in various applications, including automobiles, industrial machinery, and aerospace systems. They play a crucial role in transferring power while allowing for movement, making them essential for efficient operation in many mechanical systems.