Frequency refers to the number of cycles or repetitions of a periodic phenomenon, such as a wave, per unit of time. One hertz represents one cycle per second.

For example:

* Sound waves: The frequency of sound waves determines the pitch of a sound. Higher frequencies correspond to higher pitches.

* Electromagnetic waves: Light waves have frequencies in the visible spectrum, and radio waves have frequencies in the radio spectrum.

* Electrical signals: The frequency of an alternating current (AC) signal determines how often the current changes direction.