The Delta Quadrant is the common designation for one-quarter of the Milky Way Galaxy. Its boundary is defined by a meridian passing through the galactic core and the Sol System, and a second meridian 90° perpendicular at the core. Its closest point to Earth is located approximately 30,000 light years away.
The first recorded exploration of the Delta Quadrant was by the USS Raven (NAR-32450) which followed a Borg cube into a transwarp conduit. (VOY: "Dark Frontier") The first Starfleet mission into the Delta Quadrant occurred during an inspection of the Barzan wormhole in 2366. (TNG: "The Price") In 2378 the USS Voyager (NCC-74656) traversed the Delta Quadrant and return home.(VOY: "Endgame") In 2379 Starfleet received an distress call from the Talaxian colony. The USS Expedition (NCC-76277) would be sent, and within 2 years, Deep space 10 would be constructed.