Frequency is the number of vibrations passing a fixed point in a given amount of time, and it is measured in Hertz. One Hertz equals one cycle per second. Kilohertz (kHz), megahertz (MHz), gigahertz (GHz), and terahertz (THz) are common multiples of Hertz used to express higher frequencies. For instance, 1 kHz = 1000 Hz, 1 MHz = 1,000,000 Hz, and so on.
It is used in telecommunications for radio frequencies, in physics for studying wave properties, in music for tuning instruments, and in electronics for signal processing and circuit design.