A Charged Vacuum Emboitment or CVE served as a transit point between our universe, N-Space, and its smaller counterpart, E-Space.
The violent formation of CVEs caused holes to be punched into realities. (CC: The Invasion of E-Space)
History
The Logopolitans created CVEs using Block Transfer Computations in order to save N-Space, their universe, the existence of which was threatened by entropy. (DW: Logopolis)
CVEs contained layers of highly charged quantum particles suspended in pockets of super-vacuums. They had no external energy signature and had no detectable footprint in the three primary dimensions, however passing through one caused disorientation.
While all complex systems eventually break down, the Logopolitans reasoned that if they opened up a closed system (N-Space) in a smaller one (E-Space) they could extend the life of the larger one. By the year 1981, N-Space would have already passed the point of no return into heat death without the CVEs keeping it still viable. CVEs operate passively, drawing both physical objects and entropy through them. Because of their special function, the closure of the CVEs would threaten the physical integrity of N-Space and all life within. (DW: Logopolis, NA: Timewyrm: Apocalypse)
While in flight, the Doctor's TARDIS travelled through a CVE into E-Space by accident (DW: Full Circle). They wandered this universe for months searching for another. (CC: The Invasion of E-Space) In the middle of the 22nd century a similar event may have happened to the Human ship Hydrax, which passed into E-Space, though the King Vampire had some involvement in bringing them through. (DW: State of Decay / NA: Lucifer Rising)