1. A type of electronic modulation in which the phase of a carrier wave is varied in order to transmit the information contained in the signal.
2. Varying the angle of a wave in a carrier in order to transmit analog or digital data.

For digital signals, phase modulation (PM) is widely used in conjunction with amplitude modulation (AM); for example, quadrature amplitude modulation (QAM) uses both phase and amplitude modulation to create different binary states for transmission.