- The speed at which a wave whose phase is constant propagates through a given medium. It is the velocity at which given points within it, such as crests and troughs, travel. In a vacuum it is equal to the product of the frequency and wavelength. In a dispersive medium the phase velocity of electromagnetic waves varies as a function of the frequency, while in a non-dispersive medium the phase velocity is independent of the frequency. Also called phase speed.
- synonymphase speed