Hertz

Definition

Hertz is used to measure the frequency of sound waves as well as electromagnetic waves (light and radio waves). Since Hz is the SI unit for cycles per second, the frequency can be found by choosing a time frame (second, minute, hour) and measuring how many cycles occur during that time frame. The base measurement is 1 Hz which is equal to 1 cycle per 1 second. Adding a prefix to the Hertz provides a range of measurements from the tiniest fraction of a cycle per second to the largest cycle imaginable.

Source: http://joanwz.hubpages.com/hub/Frequency-Hertz-and-Waves