A TARDIS (Time and Relative Dimension in Space) is a space-time vehicle used by the Time Lords. As often said by the Doctor's companions, it is "bigger on the inside". The inside of a TARDIS is in a seperate dimention of the outer covering, created by the Chameleon Circuit, which helps the TARDIS blend in with the surroundings. A TARDIS moves through time and space by "disappearing there and reappearing here" also known as materialisation. A TARDIS can also fly, if the time stream stays the same.