Chameleon Circuit

Camouflage

"It’s camouflage. It’s disguised as a police telephone box from 1963. Every time the TARDIS materialises in a new location, within the first NANOSECOND of landing, it analyses its surroundings, calculates a 12-dimensional data map of everything within a 1000-mile radius, and determines which outer shell would blend in best with the environment. And then it disguises itself as a police telephone box from 1963" - The Doctor

Everyone knows that the Doctor's TARDIS is a 1960's British Police Box, when we hear the word TARDIS that is the image that appears in our head.  However it wasn't meant to look this way, not permanently anyway.  The Doctor stole his TARDIS from Gallifrey,  it's a now obsolete Type 40, mark 1 and very early on in their travels the part of the TARDIS that creates the camouflage, The Chameleon Circuit, broke leaving it stuck in this shape. What I find absolutely amazing now is that if you show a child a picture of a police box they know that it is a police box...they know that it is a TARDIS, if it wasn't for Doctor Who, this is a piece of British history that would be long forgotten.  You would show a child a picture of a Police Box and they would say "what's that" but Doctor Who, this long running, science fiction show has kept the Police Box alive in our memories.

So there's also a band called Chameleon Circuit  listen here 

C is for Camouflage