From the Wikipedia entry on the CMBR dipole anisotropy (emphasis mine),
From the CMB data it is seen that the earth appears to be moving at 368±2 km/s relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB). The Local Group (the galaxy group that includes the Milky Way galaxy) appears to be moving at 627±22 km/s in the direction of galactic longitude l = 276°±3°, b = 30°±3°.[82][10] This motion results in an anisotropy of the data (CMB appearing slightly warmer in the direction of movement than in the opposite direction).[83] From a theoretical point of view, the existence of a CMB rest frame breaks Lorentz invariance even in empty space far away from any galaxy.[84] The standard interpretation of this temperature variation is a simple velocity red shift and blue shift due to motion relative to the CMB, but alternative cosmological models can explain some fraction of the observed dipole temperature distribution in the CMB.[85]
What does the bold sentence mean?
