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, its teeth push against the rack, causing it to move in a straight line. This system is commonly used in various applications, such as in steering mechanisms of vehicles and in machinery for precise positioning. The simplicity and efficiency of the rack and pinion make it a popular choice in engineering and design, providing reliable movement in many devices.