The homeworld of the warp capable Orions, Orion was an inhabited planet in the Orion system located in the Orion sector of the Alpha Quadrant. (Star Trek VI: The Undiscovered Country, production art; TNG: "Conspiracy", display graphic)
Orion once harbored a highly advanced civilization whose history had drawn great interest from Federation historians and archaeologists alike. During the mid-23rd century, noted Federation archaeologist Doctor Roger Korby translated medical records from the Orion ruins that helped revolutionize modern immunization techniques and were required reading at Starfleet Academy. In 2269, through the assistance of the Guardian of Forever, Starfleet officers Captain James Kirk, Commander Spock and historian Lieutenant Erickson traveled to the dawn of Orion's civilization to view the planet's history unfold firsthand. (TOS: "The City on the Edge of Forever", "What Are Little Girls Made Of?"; TAS: "Yesteryear")
Devna, an Orion trapped in Elysia, told Kirk that she wished to return through the time barrier and see Orion again. Kirk offered to take her back with him, but she declined, stating that she had accepted where she now was in life. (TAS: "The Time Trap")
In 2372, Ferengi entrepreneur Quark attempted to smuggle kemocite on a highly-profitable side trip to Orion under the guise of taking his ship, Quark's Treasure, on a test flight to Earth. This proved to be unsuccessful due to sabotage. (DS9: "Little Green Men")
According to Star Trek: Star Charts (pgs. 36, 45, 60), the planet Orion was located in the Pi 3 Orionis system. This planet was visited by Zefram Cochrane on his final voyage in 2120. Orion was a non-aligned world before and after 2161, the founding date of the Federation. In 2378, Orion was a destination on the major space lanes.