group speed

noun

1. physics the speed at which energy is propagated in a wave. This is the quantity determined when one measures the distance which the radiation travels in a given time. In a medium in which the speed increases with wavelength the group speed is less than the phase speed, and vice versa

Example Sentences

In a vacuum there is no dying out of the waves, so that the group-speed and the wave-speed are identical.

From Project Gutenberg