From Lexicanum

This article needs work on its citations. For help on citation see the citation guidelines. You can help Lexicanum by fixing it.

Realspace (also known as the Materium) is the dimension where corporeal beings live; the physical plane of existence, as opposed to the Warp or warpspace. Realspace abides by all the laws of physics we know today.

The Warp on the other hand is another dimension where daemons and other warp-entities exist. They lust to cross over to realspace to feed on the souls of mortals, and on the terror their presence causes.

To travel through realspace is relatively slow and the greatest achievable speed is the speed of light (lightspeed). Therefore many intelligent species travel through the warp using warp drives or something similar.

Certain regions within the Milky Way exist where the Warp and realspace are 'fused.' The most infamous one is the Eye of Terror.