THE HERTZ
 

The standard unit of frequency is the hertz, symbolized Hz. It was formerly called the cycle per second or simply the cycle. The hertz is a small unit in the real world, and 1 Hz represents an extremely low frequency. Usually, frequency is measured in thousands, millions, billions, or trillions of hertz. These units are called kilohertz (kHz), megahertz (MHz), gigahertz (GHz), and terahertz (THz), respectively. In terms of SI units, the hertz is mathematically simple, but the concept is esoteric for some people to grasp: It is an inverse second (s^-1) or per second (/s).