Plane

A plane of existence (also often called densities or, less commonly, dimensions) are realities or parts of reality existing in parallel to each other. Planes don't necessarily have to be physical, and some visited via astral projection are reported to consist entirely of a single concept, such as an emotion.

Common Planes
Though belief systems can vary wildly, many traditions hold the following seven:
 * Physical plane
 * Emotional or Astral plane
 * Causal or Mental plane
 * Unity or Buddhic plane
 * Spiritual plane
 * Divine plane
 * Monadic or Logoic plane

Sub-planes
The astral, mental, and spiritual planes are all reported to have what are known as sub-planes, divisions within the plane distinguishing parts which act as though they were planes in their own right, but all share characteristics of their parent plane.