The Void

The Void was what the Time Lords called the emptiness between parallel universes. It was known to the Eternals as "'the Howling" and to others as "Hell".

The Void contained no temporal or spatial dimensions, but spatial language might have been used to conceptualise it. For example, the Tenth Doctor confirmed that the Void had no "up" or "down", but spoke of the universes within it being "stacked" on top of each other. Even "time" in most senses didn't actually exist there. (TV: Army of Ghosts) If someone travelled through the Void, they would have absorbed background radiation, which the Doctor called Void stuff. (TV: Doomsday)

Void life
Reportedly, little life existed in the Void, one example being the Terrordactyls (GAME: The First Adventure), although millions of Daleks and Cybermen were trapped there after being sucked in. (TV: Doomsday, The Next Doctor) A handful of Cybermen later escaped using stolen Dalek technology. According to the Tenth Doctor, due to the events surrounding the reality bomb, everything in the Void perished. (TV: The Next Doctor)

Chronomites lived in the Void naturally. (GAME: TARDIS) According to ancient Gallifreyan myth, the Mi'en Kalarash inhabited "the wasteland between realities". (AUDIO: House of Blue Fire) The Terrordactyls were native to the "Great Space-Time Void". (GAME: The First Adventure) A memory changing alien known as Adam Smith claimed to have escaped from the Void. (TV: Adam)

Void travel
A Void Ship was a spaceship which could travel through the Void into other dimensions. While the Time Lords believed this to be only a theoretical concept, it was eventually discovered that the Daleks were in possession of a powerful Void Ship in the form of a bronze sphere. (TV: Army of Ghosts)

The Cult of Skaro travelled to the Void to escape the impending destruction of the Dalek Empire in the Last Great Time War by the Doctor, taking with them the Genesis Ark, a prison ship containing millions of Daleks. They hid in the Void until the time was right. (TV: Doomsday)

This Void Ship caused a crack in the universe, making travel from one dimension to the next easier, allowing both the Doctor's TARDIS (not a Void ship) to travel to the dimension of the parallel Earth Cybermen, and those Cybermen to travel to the dimension of the Doctor. (TV: Rise of the Cybermen, Army of Ghosts)

As the Battle of Canary Wharf raged throughout London, the Tenth Doctor widened the breach of the Void. This sucked all of the invading Cybermen and Daleks into it. The breach then permanently sealed itself. (TV: Doomsday) The reality bomb used by other Daleks later weakened the dimensional walls, allowing some Cybermen to escape the Void. The rest, along with the Daleks, perished, according to the Doctor, as a result of the events surrounding the Reality Bomb. (TV: The Next Doctor)

When the Eleventh Doctor was, for a time, erased from existence by stepping into the cracks, River Song described him as being condemned to the Void between worlds. (TV: The Big Bang)

Other information
One of Rassilon's titles was "Ravager of the Void". (AUDIO: Neverland)