Nimbus III was the inhabited third planet in its star system. It was orbited by at least two moons. Nimbus III was established as a "Planet of Galactic Peace" in 2267 after the Federation-Klingon War. (Star Trek V: The Final Frontier)
In 2371, the location of Nimbus III was labeled in the star chart Data and Picard were studying in stellar cartography aboard the USS Enterprise-D. It was also labeled on a star chart in astrometrics on USS Voyager in 2376. (Star Trek Generations, okudagram, VOY: "Child's Play", okudagram)
In 2267, after the war, the United Federation of Planets and the Klingon and Romulan Empires agreed to mutually develop the planet, in the hopes that it would serve as a model for a new age of peace and understanding. An advertisement broadcasted from the planet claimed it to be "…famous for its wildlife and the fishing is terrific." Individuals who wished to move to this planet could finance their trip through Federation Federal. In reality, the planet was a desert world and the colonists chosen for the undertaking were among the most unscrupulous individuals in the galaxy, quickly taking to fighting amongst each other, fashioning their own crude weapons after the planetary government forbade weapons from them.
In 2287, the Human St. John Talbot was the Federation representative stationed on Nimbus III; General Korrd was the Klingon representative, and Caithlin Dar the Romulan. Their "office" was in the backroom of the The Watering Hole saloon. All three were captured and telepathically brainwashed by the renegade Vulcan Sybok when his "Galactic Army of Light" took over the planet's capital and only settlement, Paradise City. By taking the representatives hostage, his plan was to attract a starship to the planet, that he would commandeer to take them all to the planet thought to be Sha Ka Ree.
The USS Enterprise-A and Klaa's Bird-of-Prey responded to the hostage crisis. The Enterprise-A was commandeered by Sybok. Captain Klaa followed them, after intercepting a distress call from Captain James T. Kirk. (Star Trek V: The Final Frontier)
According to Star Trek: Star Charts (p. 66) and Stellar Cartography: The Starfleet Reference Library ("Stellar Cartography", pp. 18-19; "Federation Historical Highlights, 2161-2385”), there was a star system named Nimbus, in which this planet might possibly have been located, in the Beta Quadrant. The system's primary was a F-class star.
The computer game Star Trek Online originally placed the Nimbus system in the Nimbus sector at the junction between the Federation, the Klingon Empire and the Romulan Star Empire. Its location was subsequently changed to be very near the Romulan system, and far from the Klingon border.
According to Federation: The First 150 Years, the idea of cooperating with the Klingon and Romulan Star Empires in colonizing and developing Nimbus III was the brain child of Ambassador Robert Fox. It is stated that Fox later "regretted the whole thing," and James Kirk is quoted as saying "most of us knew Nimbus III was a joke."