A TARDIS ('Time And Relative Dimension In Space') is a hyperdimensional spaceship used by the Time Lords of Gallifrey in the fictional universe of Doctor Who. TARDISes are capable of travelling through both time and space, of altering their external appearance to blend in with their surroundings, and are famously "bigger on the inside than on the outside". Best known by far, as simply "The TARDIS", is The Doctor's means of transport, which is 'stuck' in its camouflage from 1960s Britain of a blue police telephone box – a device long-since out of use in the real world, meaning the appearance is now iconic to Doctor Who.
The Doctor's timeship, as a location, gave its name to Tardis Interlude I and II.
Within both the established continuity of the show, and that created in Atlantean Publishing stories, other Time Lords – such as Alban – have their own. According to the story For Want of Spironium..., a TARDIS requires spironium to function.
Though the name is an acronym, and hence often capitalised, it is not infrequently written as 'Tardis'.
A late development in TARDIS technology is TARDISes capable of taking human form. Examples in the fiction include Lucy, Alban's TARDIS (seen in The Testament of a Time Lord, Harvest of the Corn and Loose Threads, and referred to in The Broken Seal; her origin is revealed in Broken Mirror and she reappears in later instalments of the Mirror Quartet) and Mirilee, Xastaroth's TARDIS (also seen in Testament and a key figure in Harvest).