Dark Space is the void between galaxies. It remains largely unexplored because of the lack of stars in the area, making it incredibly difficult to explore without running out of fuel. Only a handful of space-faring races have developed way to cross Dark Space without the use of jumpgates.
The stars near the edge of the galaxy and outside have a much lower metallicity than the stars within the galaxy. As a result, planetary systems in Dark Space are rare, and even fewer have life. Planets around in Dark Space or the edge of the galaxy will be limited primarily to microbes, and most rocky planets in Dark Space are actually rogue planets that were careened outside of the galaxy.
Because of this, crossing Dark Space and even living in it is extremely difficult with few places to gather resources. As a result, most spacefaring civilizations can be found within galaxies themselves.