Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as temporal frequency for clarity and to distinguish it from spatial frequency. Frequency is measured in hertz (Hz) which is equal to one event per second. Ordinary frequency is related to angular frequency (in radians per second) by a scaling factor of 2π. The period is the interval of time between events, so the period is the reciprocal of the frequency.
|SI unit||hertz (Hz)|
|In SI base units||s−1|
For example, if a heart beats at a frequency of 120 times a minute (2 hertz), the period, T—the interval at which the beats repeat—is half a second (60 seconds divided by 120 beats). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.