A planet in the mirror universe where Gabriel Lorca sought allies after his failed coup against the Emperor, and above which the accident that sent him into the prime universe took place.
Priors World is a planet in the mirror universe, mentioned in the Discovery episode What's Past Is Prologue. It is not shown on screen, but it is central to the story of how the mirror Gabriel Lorca came to command the USS Discovery.
After his attempt to overthrow Emperor Philippa Georgiou fell apart, Lorca went to Priors World to gather support. While he was there the Emperor's flagship, the ISS Charon, caught his ship, the ISS Buran, in orbit.
Lorca was beaming back to the Buran when an ion storm struck, and the transporter accident threw him into the prime universe, where he took the place of his counterpart. From there he steered Discovery and its spore drive towards a way home, a plan that the first season slowly uncovers.