The hertz (Hz) is the SI base unit of frequency, defined as one cycle per second, measuring how often a repeating event occurs. From AC power grid frequency (50 or 60 Hz) to audio tones and processor clock speeds, hertz is the universal language of frequency. One hertz equals exactly one cycle per second.

The megahertz (MHz) equals one million hertz, widely used for radio frequency bands, early CPU clock speeds, and wireless communication standards. FM radio broadcasts in the 88–108 MHz range, while early personal computers operated at just a few MHz. One megahertz equals 1,000,000 cycles per second.