TARDIS

TARDIS (Time and Relative Dimension in Space)  is a product of the advanced technology of the Time Lords, an extraterrestrial civilization to which the program's central character, the Doctor, belongs. A properly maintained and piloted TARDIS can transport its occupants to any point in time and any place in the universe. The interior of a TARDIS is much larger than its exterior, which can blend in with its surroundings using the ship's "chameleon circuit".

The unpredictability of the TARDIS's short-range guidance (relative to the size of the Universe) has often been a plot point in the Doctor's travels. Also in "The Doctor's Wife", the TARDIS reveals that much of this "unpredictability" was actually intentional on her part in order to get the Doctor "where [he] needed to go" as opposed to where he "wanted to go".