The mirror universe counterpart of Deep Space 9, an ore processing station orbiting Bajor that is ruled by Intendant Kira for the Klingon-Cardassian Alliance and later seized by the Terran rebels.
In the mirror universe the Cardassian-built station above Bajor never became Deep Space 9. When Kira and Bashir stumble into that universe in Crossover, Terok Nor is still a working refinery in which Terran slaves process ore under the eye of the Intendant, Kira's counterpart, with Garak as her deputy and a brutal Odo as overseer.
Sisko is taken there in Through the Looking Glass to impersonate his dead counterpart and win the scientist Jennifer Sisko over to the rebellion. By Shattered Mirror the rebels have captured the station and are building their own Defiant there, with which they drive off Regent Worf's fleet.
The station is seen again in The Emperor's New Cloak, by which time it serves as the main base of the Terran rebellion.