Group velocity is the gradient of angular frequency with respect to wavevector, . It gives the leading propagation velocity of a narrow wave packet.
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Group velocity is a concept in wave theory that refers to the velocity at which the overall shape of a group of waves (or wave packets) travels through space. It is particularly important in the context of wave phenomena, such as light, sound, and water waves, and is often distinguished from phase velocity, which is the speed at which individual wave crests (or phases) move.