In “Doctor Who,” the Doctor’s time-and-space machine is the TARDIS. The name is an acronym for “Time And Relative Dimension in Space,” though “Dimensions” has also been used in the series and related material.
The TARDIS is a spacecraft and time machine belonging to the Time Lords of Gallifrey. It first appeared in the 1963 episode “An Unearthly Child,” and the Doctor’s particular TARDIS has remained the show’s central vehicle across many regenerations and eras.
Its famous exterior resembles a blue British police box. That appearance is the result of a malfunctioning chameleon circuit, which should have allowed the TARDIS to disguise itself in different surroundings. The machine is famously “bigger on the inside,” with a vast, changeable interior surrounding its central console.
A common mix-up is to call the TARDIS merely a spaceship or to confuse it with other fictional time machines such as the DeLorean. The TARDIS travels through both time and space, and its characteristic dematerialization sound is one of Doctor Who’s signature effects.