Group velocity is a concept in physics that describes the velocity at which the envelope or modulation of a wave travels through space. It is a key parameter in the study of wave packets, which are localized waveforms composed of multiple individual waves with different frequencies.

Here are key points about group velocity:

Wave Packet Composition: A wave packet is a short-lived, localized disturbance that can be constructed by combining waves of different frequencies. The group velocity represents the velocity of the overall waveform, considering the combined effect of its constituent waves.

Dispersion: Group velocity is particularly important in the study of dispersive media, where different frequencies of a wave propagate at different speeds. In dispersive materials, the group velocity is the speed at which the peak or envelope of the wave packet moves.

Relation to Phase Velocity: Group velocity is related to, but not necessarily equal to, the phase velocity of the individual waves within the packet. In non-dispersive media, group velocity equals phase velocity.