Time And Relative Dimension(s) In Space
That's what it stands for. But more importantly it's the home of Doctor Who. And I am a massive massive Doctor Who fan!
The TARDIS is in the shape of an old-fashioned British police-box. It was meant to blend in with its surroundings and cannot easily be spotted. It can take any form, however during the Doctor's timetravels somewhere in the sixties, the fuse got burnt or something and the TARDIS remained in this form.
There are still a few old police-boxes left in Great Britain and I actually saw one on Earl's Court Road, but I didn't take a photo. I might do next time though...