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"
Herschel Views the Milky Way
16/10/2009
With a 3.5 meter diameter mirror, larger than the Hubble Space Telescope, Herschel is ESA's new infrared observatory. The space-based telescope is named for German-born British astronomer Frederick William Herschel who discovered infrared light over 200 years ago. In initial tests, Herschel's cameras have combined to deliver this spectacular view along the plane of the Milky Way in the constellation of the Southern Cross. Spanning some 2 degrees the premier, false-color, far-infrared view captures our galaxy's cold dust clouds in extreme detail, showing a remarkable, connected maze of filaments and star-forming regions. These and planned future Herschel observations are intended to unravel mysteries of star formation by surveying broad areas of the galactic plane.