The Galactic Plane is the plane through space in which the stars of the Milky Way sit. The term is often used in general descriptions of the position of astronomical objects near the galaxy, e.g., the general position of a particular Globular Cluster. The term is also used in relation other flat galaxies.
The term is also used for a precisely-defined plane through the Milky Way that is an element of the Galactic Coordinate System and is based on a determination of the plane closest to the general concept. The visible Milky Way is close to flat, but does have some thickness. Galactic Equator is essentially a synonym for galactic plane, or more specifically may refer to the corresponding great circle around the Celestial Sphere. The Galactic Poles are directions from the center of the Milky Way (Galactic Center) perpendicular to the plane.