A rack and pinion is a mechanical system that converts rotational motion into linear motion. It consists of a round gear, called the pinion, which engages with a flat, toothed bar known as the rack. When the pinion rotates, it moves the rack back and forth, allowing for precise control in various applications. This system is commonly used in steering mechanisms of vehicles, where turning the steering wheel (the pinion) moves the wheels (the rack). It is also found in machinery, robotics, and various tools, providing efficient movement and positioning in a compact design.