A ratchet mechanism is a device that allows motion in one direction while preventing motion in the opposite direction. It typically consists of a toothed wheel, called a ratchet wheel, and a lever or pawl that engages with the teeth. This design enables the mechanism to advance step by step, making it useful in various applications. Ratchet mechanisms are commonly found in tools like socket wrenches and bicycle freewheels. They are also used in machinery and clocks, where controlled movement is essential. The simplicity and effectiveness of ratchet mechanisms make them a popular choice in engineering and everyday devices.