Most everyone is familiar with the drop in pitch of a train whistle as a train passes your position and switches from moving toward you to moving away from you. This phenomenon is called the Doppler Effect. The Doppler effect occurs for any wave motion, so it occurs for light as well as sound.
The shift to larger wavelengths by motion away from the observer is called a red shift by astronomers and a shift to shorter wavelengths caused by motion toward the observer is called a blue shift.
The terminology is borrowed from the visible part of the spectrum where blue is toward the short wavelength end and red is toward the long wavelength end, but the Doppler effect occurs for all wavelengths of light, not just the visible spectrum.