The kilohertz, abbreviated kHz or KHz*, is a unit of alternating current (AC) or electromagnetic (EM) wave frequency equal to one thousand hertz (1,000 Hz). The unit is also used in measurements or statements of signal bandwidth.
An AC signal having a frequency of 1 kHz is within the range of human hearing. If a signal at this frequency is input to a headset or loudspeaker, the resulting tone has a pitch that falls into the so-called "audio midrange." An EM signal at a frequency of 1 kHz has a wavelength of 300 kilometers, or about 190 miles. The standard amplitude-modulation (AM) broadcast band extends from 535 kHz to 1,605 kHz. Some EM transmissions are made at millions of kHz.
The kilohertz is a relatively small unit of frequency; more common units are the MHz, equal to 1,000,000 Hz or 1,000 kHz, and the GHz, equal to 1,000,000,000 Hz or 1,000,000 kHz.
The kilohertz is often used to specify bandwidth for digital as well as analog signals. The bandwidth of a digital signal, in kilohertz, 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 modem operating at a speed of 28,800 bps has, in a certain sense, a nominal frequency of 28.8 kHz. But the bandwidth is generally much smaller, because it depends on variations in the individual data characters, not on the number of data bits per unit time.
* The engineer's society, IEEE, and most other sources prefer "kHz" to "KHz." This apparently makes it less likely that users will confuse "kilo" (decimal 1,000) with the computer "K" (1,024).