Meta-Setting: Dungeons and Dragons Settings
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Planescape is the setting within Dungeons & Dragons that serves as the planar cosmology for the D&D worlds in 1st-3rd editions of the game. It is also known as the Great Wheel Cosmology.

Planescape refers to the planes outside of the Prime Material Plane. Individual campaign worlds, such as Oerth or Toril, have their own world pages. Other worlds on the prime material plane that do not serve as a campaign setting are part of the Spelljammer setting.

Worlds and Planes in Planescape