The Void

"The Dead Space. Some people call it hell."

- The Doctor.

The Void is the space between universes. "The Void" is only the name given to it by the Time Lords, it was also known to the Eternals as "the Howling", and to others as "Hell."

Rassilon was (amongst other titles) "Ravager of the Void". (BFA: Neverland)

It contains no temporal or spatial dimensions, but language which employs them may be used to conceptualise it. For example, the Doctor confirms that the Void has no 'up' or 'down', but also talks about the universes within it being 'stacked' on top of each other. (DW: Army of Ghosts)

Void travel
A Void Ship is a spaceship which can travel through the Void into other dimensions. While originally believed to be only theoretical by the Time Lords, it was eventually discovered that the Daleks were in possession of a powerful Void Ship in the form of a golden sphere. (DW: Army of Ghosts)

The Cult of Skaro travelled to the Void to escape from 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, and hid in the Void until the time was right. (DW: Doomsday)

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

After the Battle of Canary Wharf raged throughout London, the Doctor sucked all of the Cybermen and Daleks into the Void, without anyone else falling in(DW: Doomsday)

Other information
The memory changer "Adam Smith" said he had been trapped in the Void for a long period of time. (TW: Adam)
 * It is not confirmed if this was the same 'Void'.