Deep Darkness

From TARDIS Index File, the free Doctor Who reference.

The Deep Darkness was either a void, a pocket universe, or some kind of dimension that existed outside this universe. During the Dark Times of the universe, the Eternals banished the witch-like Carrionite-race and the Hervoken to the Deep Darkness. It is found in the Rexel planetary configuration at the co-ordinates '5/930167.02'.

Three Carrionites escaped from the void and in 1599 opened a gateway between Earth and the Deep Darkness. All trapped Carrionites began to enter Earth when the gateway was closed by the brillant words of William Shakespeare. (DW: The Shakespeare Code)

Judging by its desciption, the Deep Darkness may in fact be the Void.