Terok Nor orbiting Bajor.
The Defiant under construction at Terok Nor.
In the mirror universe, Terok Nor was a space station built under the authority of the Klingon-Cardassian Alliance in orbit of Bajor. In 2370, the station was the command post for Alliance authority throughout the Bajor sector, under the command of Intendant Kira Nerys. The station also served as a processing center for uridium ore mined from Bajor; the processing facilities were manned by Terran slaves. Terok Nor still orbited Bajor in the Mirror Universe because the wormhole was still unknown there.
In 2372, the Terran Rebellion wrestled control of the space station away from the Alliance. The Alliance, determined to recapture the station, sent a fleet of ships under Regent Worf to fight the rebels. When they arrived, the rebels had completed their Defiant which was based on schematics for the Defiant in the primary universe. The Alliance fleet was defeated and Terok Nor remained a base of operations for the Terran Rebellion for at least the next three years.
Apocrypha
In the Deep Space Nine book trilogy Millennium, a possessed Dukat hides in the Mirror Universe Terok Nor, awaiting his final confrontation with Weyoun, Kai of the Pah-wraiths. In the book, Dukat turns the mirror Terok Nor into a house of horrors.
In the Mirror universe anthology Obsidian Alliances, the fact that Terok Nor can remain the center of the Terran Rebellion even though it orbits Bajor is explained by saying that the station will bombard Bajor if it is attacked, killing billions and devastating the Bajoran environment for centuries and forcing Bajor to prevent attacks on Terok Nor by the Klingon-Cardassian Alliance.