What are Planes?
Planes are worlds or collections of worlds which function with their own set of laws governing how fundamental sources, such as magic, electricity, gravity, even direction, are defined.
Planes are immense and infinite. A subcategory of planes are demiplanes which are limited by definite borders. Nobody knows the exact number of planes – could be less than infinite, but the last person to go out counting hasn’t come back yet.
A Map of the Planes
The Three Truths of the Planes
The following three basic rules pretty much describe the entire structure of the multiverse.