In the most general sense, frequency is defined as the number of times an event occurs per unit of time. In physics and chemistry, the term frequency is most often applied to waves, including light, sound, and radio. Frequency is the number of times a point on a wave passes a fixed reference point in one second.

The period or duration of time of a cycle of a wave is the reciprocal (1 divided by) of frequency. The SI unit for frequency is the Hertz (Hz), which is equivalent to the older unit cycles per second (cps). Frequency is also known as cycles per second or temporal frequency. The usual symbols for frequency are the Latin letter *f* or the Greek letter ν (nu).

### Examples of Frequency

Although the standard definition of frequency is based on events per second, other units of time may be used, such as minutes or hours.

- For example, a human heart may beat at a frequency of 68 beats per minute.
- A 78 record on a turntable turns at the rate of 78 revolutions per minute or 78 rpm.