A kilohertz is a unit for measuring how fast something repeats: how many times it happens each second. That kind of counting is called frequency. One kilohertz is 1,000 hertz, which means 1,000 times a second. People use it a lot for sound and for radio signals. A deep hum might be measured in hertz; many AM radio stations are still given in kilohertz. The short form is kHz. Unlike a kilobyte, this kilo- is the ordinary science kilo-: it is exactly 1,000, not 1,024. Hertz is named after a scientist. After a number, technical English usually keeps the same form: “800 kilohertz,” not “800 kilohertzes.” Though actually, FM radio is usually talked about in megahertz, a much bigger step; if you put an FM station in kilohertz, the number will look strangely huge.