Galactic Plane
The Galactic Plane is the plane in which the majority of a disk-shaped galaxy's mass lies. In the case of the Milky Way, it is the plane of the galaxy's disk, encompassing the spiral arms, stars, gas, and dust. This plane is used as the reference for the galactic coordinate system.
Source: asd.gsfc.nasa.gov
APODs including "Galactic Plane"
7,000 Stars And The Milky Way
23/05/1998
This panorama view of the sky is really a drawing. It was made in the 1950s under the supervision of astronomer Knut Lundmark at the Lund Observatory in Sweden. To create the picture, draftsmen used a mathematical distortion to map the entire sky onto an oval shaped image with the plane of our Milky Way Galaxy along the center and the north galactic pole at the top. 7,000 individual stars are shown as white dots, size indicating brightness. The "Milky Way" clouds, actually the combined light of dim, unresolved stars in the densely populated galactic plane, are accurately painted on, interrupted by dramatic dark dust lanes. The overall effect is photographic in quality and represents the visible sky. Can you identify any familiar landmarks or constellations? For starters, Orion is at the right edge of the picture, just below the galactic plane and the Large and Small Magellanic Clouds are visible as fuzzy patches in the lower right quadrant.