The Void

The Void was what the Time Lords called the emptiness found between all parallel universes, different dimensions, and other realities. It was known to the Eternals as "'the Howling" and to others as "Hell".

The Void contained no light or darkness. It also featured no temporal or spatial dimensions (neither "up" nor "down"), but the Tenth Doctor used some spatial language to conceptualise how the Void was "in between" all the universes which were "stacked up against each other". Even time in most senses did not actually exist there. Anyone who entered the Void could choose to let eternity pass them by: they would "exist outside the whole of creation" and would be completely unaffected by events as major as the end of their home universe or the start of another. (TV: Army of Ghosts)

All material which travelled through the Void absorbed a particular type of harmless background radiation, which the Doctor called Void stuff. The longer a material had been present within the Void, the more "Void stuff" it became saturated with. (TV: Doomsday)

Void life
The Tenth Doctor asserted that no life existed naturally inside the Void. This did not stop Daleks (led by the Cult of Skaro) and also Cybermen (from a parallel universe the Doctor called Pete's World) from successfully crossing through it. (TV: Army of Ghosts)

The Twelfth Doctor discovered that the Fractures were beings that lived inside the Void, and compared them to antibodies for the multiverse. (COMIC: The Fractures)

Chronomites naturally traversed space-time "riptides" and the Void. (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)

Daleks and Cybermen in the Void
A Void Ship was a spaceship which could enter, traverse, and exit the Void into other dimensions. Even the Time Lords believed such a vessel to be a theoretical concept only, impossible to build in reality. However, in 2007, the Tenth Doctor identified one as the object around which Torchwood Tower had been constructed, and explained its significance to the befuddled human scientists. Soon it was discovered that this mysterious bronze sphere had been created by the elite four-member Dalek group known as the Cult of Skaro. (TV: Army of Ghosts)

The Cult had used it to flee into the Void to escape the impending destruction of the Dalek Empire in the Last Great Time War. Within it, they carried the Genesis Ark, a prison ship they had stolen from the Time Lords containing millions of trapped Daleks. They hid in the Void Ship until they were confident they could open the Genesis Ark. (TV: Doomsday)

The Cult's Void Ship caused a "breach" in the universe and an adjacent parallel universe, making travel between them possible. This allowed the Doctor's TARDIS (not itself a Void ship) to crash-land in the parallel universe, which he would later label Pete's World. (TV: Rise of the Cybermen)

The Dalek's Void Ship also created an unintentional "wake" which the parallel-Earth Cybermen used to cross over. (TV: Army of Ghosts)

As the Dalek force (freed from the Genesis Ark) began to exterminate the Cybermen army in the Battle of Canary Wharf, the Tenth Doctor widened only one side of the Void breach. Since they were saturated in Void stuff, all of the Cybermen and all but 4 of the Daleks were sucked back into it. The breach then permanently sealed itself. (TV: Doomsday) The four Daleks of the Cult of Skaro escaped being hurled into the Void by means of an emergency temporal shift to Manhattan in 1930. (TV: Daleks in Manhattan)

Trapped in the Void, the Pete's World Cybermen stole or scavenged two things from the Daleks who were trapped with them: intelligence about the Doctor, and a Dimension Vault. Later, the destruction of the New Dalek Empire and their reality bomb somehow triggered an unspecified cataclysm inside the Void, causing apparently all of the Time War Daleks and the Cybermen trapped there to perish. Some Cybermen were ejected from the Void beforehand, however, and used the Dimension Vault to travel to 1851 London, where they built a CyberKing. (TV: The Next Doctor)

Other information
The Fifth Doctor and Nyssa became trapped in the "dimensional interface," the "space between worlds" after escaping a collapsing time bubble. (AUDIO: The Eternal Summer)

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)

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

Le Void