Definitions for "Phase modulation"
One of three ways of modifying a sine wave signal to make it carry information. The sine or "carrier" wave has its phase changed in accordance with the information to be transmitted.
Angle modulation in which the phase of the carrier is controlled by the modulating waveform. The amplitude of the modulating wave determines the amount of phase shift, and the frequency of the modulation determines how often the phase shifts.
Modulation is the process of using a medium to carry information. A torch beam could be "modulated" by turning it on and off, thus sending digital information. An electrical sine wave travelling down a twisted wire pair can also be modulated to carry information, a sine wave that is defined by its frequency, amplitude and phase. These are the only three parameters of a sine wave that can thus be changed to carry information. Phase modulation is typical used in higher speed modems.