Frequency modulation (FM) is changing the frequency of a signal's carrier. In communications using a continuous sinusoidal signal, information can be encoded in a pattern of changes to the frequency. In FM radio, the encoded pattern is represents the pattern of air pressure changes that constitute the sounds being communicated.
Frequency modulation is used in radar, such as in chirps and in continuous-wave frequency-modulated (CWFM) radar. The latter has some of the advantages of using chirped pulses plus the advantage of having no gaps in the received information.