The Alpha Quadrant is a designation for one quarter of the Milky Way Galaxy. The United Federation of Planets defines the border between the Alpha and Beta Quadrants as running through the Sol system from the galactic edge to the centre of the galaxy. Its other boundary was joined to the Gamma Quadrant.
Several of the region powers primarily located in the Alpha Quadrant include the Federation, Cardassian Union, Breen Confederacy, Ferengi Alliance, Tholian Assembly and the Tzenkethi Coalition. The Romulan Star Empire and Klingon Empires, while primarily in the Beta Quadrant according to Federation definition also exert their presence into the Alpha Quadrant.
The bulk of the quadrant had yet to be explored by these powers by the late-24th century.
The Alpha Quadrant was connected to a point in the Gamma Quadrant by the Bajoran wormhole. The two apatures of the wormhole, the Bajor system and Idran system, were around 70,000 light years apart. (DS9: "Emissary")