A unit of speed. 1 million hertz. Millions of cycles per second. Most often used as a measurement of a PC processor chip's speed and power, with bigger numbers meaning more speed and a higher price.

The bandwidth of a digital signal, in megahertz, is related to the data speed in bits per second. In general, the greater the data speed, the larger the bandwidth. Data speed is not, however, the same thing as bandwidth. A high-speed cable or fiberoptic modem operating at a speed of 5,000,000 bps has, in a certain sense, a nominal frequency of 5 MHz. But the bandwidth is generally much smaller, because it depends on variations in the individual data elements, not on the number of data bits per unit time.