The TARDIS (Time and Relative Dimension in Space) TT Type 40 Mark 1 (Sexy) (The Doctors Wife) is a time machine.Bigger on the inside - transcendentally dimensional, made possible by transcendental engineering. Controlled via the dimensional stabiliser.
The Tardis has a chameleon circut which enables it to blend in with it's surroundings, unfortunately this tardis has a malfunction which the Doctor can't fix, so the Tardis is stuck in the form of a 1950's Police Box. Apart from Time travel, the Tardis has a telepathically based universal translation system for the travellers. The human form of the Tardis is called Idris who (or due to the short range guidance (relative to the size of the universe)) sometimes gets the Doctor to where he is needed.
Idris is played by Suranne Jones