Dark space

Dark space is the name for the void between galaxies. Dark space is empty of stars, hence the name. Because billions of light-years lie between any two galaxies, dark space is essentially a vast expanse of absolutely nothing.

The Reapers are known to reside in dark space, waiting for the vanguard left behind to open the Citadel mass relay, to permit entry by the Reaper fleet into the heart of the galaxy.