A CORDIS was the Word Lord equivalent of a TARDIS. CORDIS stood for Conveyance Of Repeating Dialogue In Space-time. (AUDIO: The Word Lord) CORDISes were described by the Seventh Doctor as a complex linquistic structure and a non physical TARDIS.
CORDISes ran on common words and phrases used throughout the multiverse and disguised themselves as such. The CORDIS chameleon circuit was called a chameleon meme by the Seventh Doctor. These disguises could be jokes, expressions, or any other kind of phrase. (AUDIO: A Death in the Family)