The term "Doppler" refers to the Doppler effect, a phenomenon observed when a wave source moves relative to an observer. This effect causes a change in frequency or wavelength of the waves, such as sound or light. For example, as an ambulance approaches, its siren sounds higher in pitch, and as it moves away, the pitch lowers. The Doppler effect is widely used in various fields, including astronomy and meteorology. In astronomy, it helps determine the speed and direction of stars and galaxies by analyzing the shift in light wavelengths. In meteorology, it is used in Doppler radar to track storm systems and precipitation.