Final answer:
Red shifts in spectral lines from distant galaxies signify that the galaxies are moving farther from us, due to the expansion of space itself.
Step-by-step explanation:
The observation of a red shift in the spectral lines of light from distant galaxies indicates that these galaxies are moving farther apart from one another. When we talk about redshift, it refers to the displacement of spectral lines toward longer wavelengths, which is a result of galaxies receding away from us. The redshift is directly proportional to the distance, meaning the farther away a galaxy is, the faster it seems to be moving away. Importantly, the redshift phenomenon is significant not just because the galaxies themselves are moving, but as a mainly because it is an indication of the expansion of space itself.