Frequency is a measure of how often a repetitive event occurs over a given period of time. It is commonly measured in units such as cycles per second (Hertz, Hz), revolutions per minute (RPM), or beats per minute (BPM). Frequency is calculated by dividing the number of occurrences by the duration of the time interval.

In physics, frequency is the rate at which a wave oscillates or a particle vibrates. It is closely related to the concept of period, which is the time taken for one complete cycle of a repetitive event. The inverse of frequency is the period, and the inverse of period is the frequency.

Frequency is an important concept in many fields, including physics, engineering, music, and medicine. In physics, it is used to describe the motion of waves and particles. In engineering, it is used to design and analyze systems that involve periodic motion. In music, it is used to describe the pitch of sounds. In medicine, it is used to measure heart rate and other physiological parameters.