The Planar Weave

The Planar Weave refers to the well of arcane energy that arcane casters tap into to cast their spells. Most supernatural abilities of monsters also use The Planar Weave as their power source. The Planar Weave is so named because most scholars believe that it represents the energy created by the planes, though the exact nature of this creation is not clear. Most scholars agree that different planes emanate distinct kinds of arcane energy. The art or school of tapping into and utilizing the arcane power of a specific plane is called a Warren.

NOTE: not all scholars, arcane schools, or religious traditions frame arcane energy as a "planar weave." Many other obscure explanations for arcane power exist, from the blood of Gods to the souls of ancestors.