Celtris III was a planet under the control of the Klingon-Cardassian Alliance during the late 24th century. It had only one settlement which was located near the equator and whose dominant population consisted of Cardassians who found the planet's warm, arid climate much to their liking. Terrans, Vulcans and a few Tellarites, and Deltans could also be found among its population and resided in the settlement's working class quarters. A few Klingons could also be found on Celtris although being stationed here was often considered to be more of a punishment than anything else.
Among the settlement's residents were Welsey and Momma Pulaski, a Terran medicine woman. The archaeologist for hire Jean-Luc Picard also frequented the settlement due to the fact that his patron Gul Madred controlled the outpost.
The Terran Rebellion was active on Celtris III as it was thought that Alliance officials were developing metagenic weapons somewhere below the settlement's surface (TNG novel: The Worst of Both Worlds)