The Alpha Quadrant is the common designation for one-quarter of the Milky Way Galaxy. Its boundary in the region around the Federation is defined by a meridian passing through the galactic core and at least near the Sol System.
The Orion Arm, Perseus Arm and Sagittarius Arms of the galaxy are located in that quadrant.
Star Trek OnlineEdit
Currently, the planets in the Alpha Quadrant are the only planets available for the game's launch.