Definitions for "Doppler shift"
A change in frequency resulting from relative motion along the line between the transmitter and the receiver. If the source and the receiver are approaching each other, the frequency received is higher than the frequency transmitted by a factor, depending on the actual relative velocity. Knowledge of this shift is used to determine the relative velocity.
The apparent change in the frequency of a wave, such as sound or light, as the source moves toward or away from the observer. The pitch (or frequency) appears to increase as the source approaches the observer and to decrease as it moves away.
The magnitude of the perceived change in the frequency of a sound due to the Doppler effect.
Keywords:  effect, see
(See "Doppler Effect").