The term "hertz," in physics, defines a standard unit of frequency measurement and is equal to one cycle per second; it is abbreviated as "Hz." It was named after Heinrich Hertz (1857-1894), a German physicist who was the first person to prove the existence of electromagnetic waves.
Hertz are often written with prefixes such as KHz (kilo, or thousands), MHz, (mega, millions), GHz (giga, billions), or THz (tetra, trillions). The wave range of audible sound is 20 to 20,000 KHz, while visible light falls between 430 and 790 THz. Computer CPU frequencies are given in gigahertz and are a measure of master clock rate.