(Photo and knitted TARDIS created by Ivy, who is incredibly talented and creative.)
The TARDIS is the blue phone booth that Doctor Who uses to travel around through time and space. I guess it used to have a cloaking device that changed its outer shell to blend in with its surroundings, but the camouflage got stuck on the police box design.
Ash said that TARDIS is an acronym. I think it stands for “Totally Awesome Rotating Device in Space.”