Edwin Hubble theorized that it indicates the speed of recession of, and the distances of, the galaxies and attributed it to the Doppler Effect.  
Martin Humason and Alan Sandage, who experimentally verified its validity as a correlative tool, offered a layman's explanation of it with their "flashlight analogy."  It is now known that, after passing a mass, photons exhibit a residual amount of it, though not the value of 5.8, which is the highest known.  Edwin Hubble theorized that it indicates the speed of recession of, and the distances of, the galaxies and attributed it to the Doppler Effect.  FTP, give this two-word term that identifies the displacement toward longer wavelengths observed in the spectral lines of astronomical objects.
Martin Humason and Alan Sandage, who experimentally verified its validity as a correlative tool, offered a layman's explanation of it with their "flashlight analogy."  
red shift