Definition: Rotations per minute (rpm) is a unit of angular speed or rotational frequency. It specifies the number of complete rotations or revolutions completed in one minute.

History/origin: The concept of measuring rotational speed has been around for centuries, particularly in mechanical engineering. The specific term 'rotations per minute' became standardized with the development of machinery and engines.

Current use: RPM is commonly used to measure the speed of rotating machinery, such as engines, motors, turbines, and spinning disks (e.g., hard drives). It is a vital parameter in mechanical engineering, automotive engineering, and various industrial applications for controlling and monitoring rotational speeds.