Transdimensional engineering
Transdimensional engineering. You can hear the description of it from Robots on File:Which box is bigger? - Dr Who - BBC sci-fi.
Talk about it here.
Transcendental engineering was the technology of creating dimensionally transcendental objects, which the Fourth Doctor proclaimed a "key Time Lord discovery". (TV: The Robots of Death) It enabled TARDISes to exist.
Other than the Time Lords, the Daleks (TV: The Chase, The Evil of the Daleks) and Mawdryn's people, who sought to emulate the Time Lords, had developed this technology and employed it in their transmat capsules. (TV: Mawdryn Undead) The Genesis Ark was known as "Time Lord science", which the Tenth Doctor elaborated was a prison ship which was bigger on the inside. (TV: Doomsday)
A young Trion officer seemed unfazed by the dimensionally transcendental interior of the Doctor's TARDIS, which suggests his species had some familiarity with this kind of science. (TV: Planet of Fire)
The War Lords possessed dimensionally transcendental space-time vessels known as SIDRATs, though only those provided by a renegade Time Lord, the War Chief. (TV: The War Games)
