Frequency Modulation is a method of conveying intelligence in wireless communications and broadcasting. The amplitude of the carrier remains constant, and the instantaneous frequency varies. One scheme for obtaining this type of modulation is to apply the modulating signal to a varactor in an oscillator. Another method is to modulate the phase of the oscillator signal. This causes small fluctuations in the frequency as well, because any instantaneous phase change shows up as an instantaneous frequency change (and vice versa). The abbreviation, FM.
See also, AMPLITUDE MODULATION, PHASE MODULATION, SINGLE SIDEBAND.