A plane is a vast dimension with various physical traits, such as gravity and chronology, and metaphysical traits, such as alignment and quintessential composition.1 Each plane in the Great Beyond represents a separate, concurrent, encapsulated universe that exists independently of each other, although most have connections linking them together.2
Each plane is effectively a standalone infinite universe, differentiating them from demiplanes, which are finite and measurable. Planes are also often traversable via means of planar travel, while demiplanes are sometimes subject to more restrictive access.3
Planes might intersect at specific coordinates of each plane's physical dimensions, making them coterminous with one another. Planar travel between the intersecting planes is possible at these points. One example in the Great Beyond is the intersection of the Material Plane and Plane of Air.3
Planes that are coterminous at every point, resulting in a total overlap between one another, are considered to be coexistent planes. The Ethereal and Shadow planes, for example, are coexistent with the Material Plane.3
Planes might be subdivided into layers, each having their own physical properties similar to distinct planes. These layered planes are interconnected in similar ways as coterminous planes, but might also have physical connections, gates, and fluid edges. Layers are usually traversed in a specific order most often visualized as a stack, with connections to other external planes occurring on the top or bottom layers. The levels of Hell represent the most prominently known example of layered planes in the Great Beyond.3
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