User blog comment:DYBAD/Character Sheet/@comment-24955665-20171103061208/@comment-4867780-20171106221422

Demi-plane are finite and relatively small portions of space-time, that are either natural byproducts of larger planes or artificial creations for specific purposes (home, workshop, prison, etc.) with restricted access controled by their creator.

Planes can be generally understood as "dimensions", they can be of any size, form and complexity, including universal/multiversal, each plane usually being both an amalgamation of smaller ones and an integral part of a greater one.