DARDIS

A DARDIS was a Dalek time machine, roughly comparable in abilities to a Time Lord TARDIS. It was dimensionally transcendent, and created for the express purpose of chasing the Doctor through time and space. One of these craft enabled the Doctor's companions Ian Chesterton and Barbara Wright to return home. The Doctor set the ship for self-destruction after it had transported them to 1965 London. (DW: The Chase)

The Daleks and Mavic Chen used a DARDIS to pursue the Doctor, his companions and the Monk. (DW: The Daleks' Master Plan)

At one point, the Master attached a "DARDIS core" to his own TARDIS console. (PDA: The Quantum Archangel)

The Daleks used taranium to power their space-time craft. (DWN: The Chase, Mission to the Unknown, The Mutation of Time)

Behind the scenes
The name "DARDIS" cannot be substantiated easily. It was never used in any televised adventure. Nor does it appear in the novelisations for The Chase, or part 1 or part 2 of The Daleks' Master Plan. Instead, author John Peel consistently uses the phrase "Dalek time-machine".

It has been alleged that "DARDIS" does appear in scripts for The Chase but it's unclear what is the source of this claim, since the script has never been made available commercially. Of the sources cited in this article, the only one that actually uses the term "DARDIS" is The Quantum Archangel, but the reference there is just a name-drop; there's no guarantee that the author is actually talking about the Dalek time-machines in The Chase.

Likewise, the meaning of the acronym DARDIS remains unknown. It is likely a contraction of "Dalek TARDIS" — or possibly "Daleks and Relative Dimensions in Space".