A unit of frequency equal to one cycle per second, used in the measurement of electrical signals and electromagnetic waves, including sound and light. Essentially, hertz is a measure of the number of times an electrical event repeats in one second, and is used to describe the "clock rate" of a computer's central processing unit (usually described—as of this writing—in megahertz, or "millions of hertz"). Hertz is abbreviated Hz, and was named for German physicist Heinrich Hertz, who first described electromagnetic waves.