A realm of endless space, filled with stars and planets that see and hunger and think and plan, with utterly alien minds that shatter the souls of any mortal foolish enough to try to catch glimpses of their demesne. The things that swim through the space between the astronomic entities are just as alien in form and mind, but they’re much closer to mortals in scale and so much more interested in the (to them) utterly bizarre goings-on in the mortal realm.
The Void impinges on the mortal realm in areas rich in entropic magics, where reality itself seems to corrode and twist upon itself and taint everything that goes there. The slimy and tentacular things that crawl through such rifts often seem to be attempting to communicate, but the meanings of what they utter have always clawed at the sanity of their listeners, leaving most mortals who know of such things to treat them as dangerous at best, and actively inimical at worst.
The few voidspawn that have managed to communicate with mortals have done so by hollowing out the minds of an unfortunate mortal and puppeting them, speaking their bizarre and deranged demands and wishes through them. What little we know of the Void comes mostly from these conversations, before the voidspawn being questioned inevitably decayed into raving and violent madness and were forcefully put down.