TARDIS:

The word TARDIS is an acronym that stands for Time And Relative Dimension In Space. A product of Time Lord technology, they are grown, not made. A properly maintained and piloted TARDIS can transport its occupants to any point in time and space. Its exterior has the ability to blend in with its surroundings through the ship's chameleon circuit.  

 Apart from the ability to travel in space and time (and, on occasion, to other dimensions), the most remarkable characteristic of a TARDIS is that its interior is much larger than it appears from the outside. The explanation is that a TARDIS is "dimensionally transcendental", meaning that its exterior and interior exist in separate dimensions. The Fourth Doctor tried to explain this to his companionLeela, using the analogy of how a larger cube can appear to be able to fit inside a smaller one if the larger cube is farther away, yet immediately accessible at the same time. According to the Fourth Doctor, transdimensional engineering was a key Time Lord discovery. To those unfamiliar with this aspect of a TARDIS, stepping inside the ship for the first time usually results in a reaction of shocked disbelief as they see the interior dimensions.

A TARDIS draws its power from several sources, but primarily from the singularity of an artificial black hole, known as the Eye of Harmony. The original Eye was located on Gallifrey, with a mathematically identical copy inside each TARDIS. They were connected in order to provide a TARDIS with power. After the destruction of Gallifrey in the Time War, the Doctor was forced to redesign his TARDIS to absorb energy from other locations, such as a space-time rift. The power source of the TARDIS, referred to as the "Heart of the TARDIS", is said to be beneath the central column of the console, with the rise and fall of the column an indication of its functioning. They are also said to draw power from the entire universe. Once, when the Doctor's TARDIS fell through a hole in the time vortex and landed in a parallel universe, it would not function without the use of a crystal power source from deep within the TARDIS, charged by the Doctor's life force.

Other elements needed for the proper functioning of the TARDIS and requiring occasional replenishment include mercury (used in its fluid links), the rare ore Zeiton 7 and "artron energy." This is a form of temporal energy, generated by Time Lord minds, which is also said to help power a TARDIS. Another form of energy, "huon energy", is found in the heart of the TARDIS and (apart from the activities of the Torchwood Institute) nowhere else in the universe.

Before a TARDIS becomes fully functional, it must be primed with the biological imprint of a Time Lord, normally done by simply having a Time Lord operate the TARDIS for the first time. This imprint comes from the Rassilon Imprimatur, part of the biological makeup of Time Lords, which gives them both a symbiotic link to their TARDIS and the ability to withstand the physical stresses of time travel. Without the Imprimatur, molecular disintegration would result. This serves as a safeguard against misuse of time travel even if the TARDIS technology were copied. Once a time machine is properly primed, however, with the imprint stored on a device called a "briode nebuliser", it can be used safely by any species. According to Time Lord law, unauthorised use of a TARDIS carries "only one penalty", implied to be death.

A TARDIS usually travels by dematerialising in one spot, traversing the time vortex, and then rematerialising at its destination, without physically travelling through the intervening space. However, the Doctor's TARDIS has been seen to be able to fly through physical space. While a TARDIS can materialise inside another, if one TARDIS occupies exactly the same space as another, a Time Ram will occur, resulting in the mutual annihilation of both. The Master once tricked the Doctor into materialising his TARDIS around the Master's, creating a dimensionally recursive loop, with each TARDIS appearing inside the other's console room.

The experiences of the TARDIS and its crew can be recorded and played back from the Matrix, the Time Lord computer network that is the repository of all their knowledge. The Doctor implies in this serial, with his protestations of being "bugged", that the TARDIS is not normally connected to the Matrix in this manner.

The TARDIS has been shown to be incredibly rugged, withstanding gunfire, temperatures of 3000 degrees without even scorching , atmospheric reentry, and falls of several miles. Once, the Third Doctor's TARDIS fell down the side of a cliff and is later found to be undamaged. He remarks that it "may have its faults, but it is indestructible." This clearly doesn't apply when facing certain advanced weaponry, such as Dalek missiles, for which the TARDIS requires additional shielding. Furthermore, the Fifth Doctor once believed the TARDIS to have been destroyed in a meteorite bombardment, apparently contradicting the earlier claim of indestructibility. Another contradiction occurs when the Tenth Doctor's TARDIS is hit in mid-flight by a space-going replica of the Titanic, creating a large hole in the interior wall. Its shields were down at the time. The Tenth Doctor later activates some controls and all damage is repaired. Shortly after this, an explosion on the Titanic cause the TARDIS to drift into space where it withstands an atmospheric reentry.