|There is more information available on this subject at Doppler radar on the English Wikipedia.|
Doppler Radar is a form of radar that uses the Doppler effect of the returned echoes from targets to measure their radial velocity. To be more specific the microwave signal sent by the radar antenna's directional beam is reflected toward the radar and compared in frequency, up or down from the original signal, allowing for the direct and highly accurate measurement of target velocity component in the direction of the beam.
Weather radars process velocities of precipitations by Pulse-Doppler radar technique, on top of their intensities. Because of this, "Doppler radar" is often wrongly used to refer to weather radars.