Electronic  transmission Frequency:

Frequency is the rate at which a wave or cycle alternates between high and low (analog mode) or on and off (digital mode). For example, the lowest buz notes reproduced on a good stereo set may emanate a wave pattern as slow as 30 times (cycles) per second, while very high notes cause wave patterns to alternate as often as 20,000 times per second. One cycle per second is called a Hertz (HZ). The enclosed table shows some frequencies for telephone and other electronic transmission media.