In Doctor Who, the Doctor’s time-traveling ship is called the TARDIS.
The name is an acronym for “Time And Relative Dimension(s) In Space.” It is both a spacecraft and a time machine belonging to the Time Lords, the Doctor’s species. Although many TARDISes exist in the Doctor Who universe, the series chiefly follows the Doctor’s own ship as it carries the Doctor and companions across history, the future, and distant worlds.
The TARDIS is famous for appearing as a blue British police box while being vastly larger inside. This is explained by its chameleon circuit, a disguise system intended to make the ship blend into its surroundings. A malfunction left the Doctor’s TARDIS stuck in the police-box form. The machine first appeared with the series in 1963, and its distinctive dematerialisation sound became one of the programme’s signatures.
A common mix-up is treating TARDIS as merely a spaceship. Its defining ability is travel through both space and time, while its “bigger on the inside” design reflects the fictional idea of dimensional transcendence.