Galactic Coordinates are sky location coordinates given with respect to the center of the Milky Way Galaxy (our galaxy). The Milky Way galaxy is a spiral galaxy - very flat with a bulging core.
Galactic coordinates are expressed in galactic latitude and galactic longitude. Galactic latitude is measured from the galactic equator north (positive numbers) or south (negative numbers); galactic longitude is measured eastward along the galactic plane from the galactic center.
From Earth, the center of the galaxy is in the constellation Sagittarius. The galactic plane lies along the 0° latitude.