Phase velocity

When a signal is propagated without distortion, the speed that a point on the waveform of this signal appears to have is called the "phase velocity" of that point. Thus, there can be a phase velocity for each point on the waveform if it is distorted over time.

More rigorously, the phase velocity is defined as the ratio of the pulse to the wavenumber associated with that pulse:

Phase velocity

For an illustration of this definition and of the difference with group velocity see the following figure.

Click on the image to see the animation.