The Orion Arm is a minor spiral arm of the Milky Way some 3,500 light-years across and approximately 10,000 light-years in length. Three of the primary systems of the four major Factions are located within the Orion Arm - Sol, Elysia and Concord.

The Orion Arm was named by astronomers on pre-Fall Terra, after the Orion constellation, which is one of the most prominent constellations of Terra's Northern Hemisphere winter (Southern Hemisphere summer). The Orion Arm is located between the Saggitarius Arm (toward the Galactic Center) and the Perseus Arm (toward the Galactic rim), the latter one of the two major arms of the Milky Way. The Sol System is the basis of the modern coordinate location system, and is considered to be 0,0, the origin point - although Sol has been designated as being located in the Trappist Sector for the sake of convenience. The Orion Arm extends lightly off the lateral on this system, and the spinward side inclines towards the galactic core. Within the Orion Arm, the Sol System lies about halfway along the Orion Arm's length, approximately 26,000 light-years from the Galactic Core.