Multiverse

Multiverse is a common slang term that refers to an over-arching "multiplicity of universes" created by the grouping of planes. An alternative term with the same meaning is Cosmology.

List of D&D Multiverses

• The Great Wheel is the oldest D&D cosmology, originating in Advanced Dungeons & Dragons and developed by the Planescape setting. It is considered the "iconic" multiverse.
• The World Tree is a cosmology unique to the Forgotten Realms setting.
• The World Axis is a cosmology invented for Dungeons & Dragons 4th Edition, and is synonymous with the Nentir Vale setting.
• The Great Beyond is the cosmology Pathfinder created for its Golarion setting, and in many ways represents a blending point of the Great Wheel and World Axis.
• The Orrery is the fan-nickname for the unique cosmology of the Eberron setting.

Assorted Multiverses

• Yog-Sothothery is a Multiverse all in its own right - and be assured, that's not good. At all. One of the core assumptions in this setting is that the human world is an illusion in a horrifying, unknowable sea that humanity can barely comprehend. Lovecraft's Multiverse is literally so insane that it's the core, overarching villain of the setting.
• Lord of the Rings has a simple one; Middle-Earth is something akin to a planet, with a separate elven "plane" where the elves go when they leave Middle-Earth behind. There's also the void beyond, which contains the Timeless Halls (where the creator god Eru resides and where, presumably, humans go after they die) and places that are not Timeless Halls and contain uncharted assorted nastiness, such as hungry deity-eating spiders and the chained, blinded and mutilated original Big Bad Evil Guy floating and waiting for the end.
• Warhammer Fantasy and Warhammer 40000 has the same overall Multiverse - A material plane where shit happens, and the Realm of Chaos, which is compromised of the four Chaos God's individual domains that border each other in impossible ways. The Realm of Chaos bleeds into the Warhammer Fantasy material plane through the Chaos Wastes in the north, slowly becoming more and more chaotic as you move to the north pole. The Realm of Chaos has a permanent gate to the material world in Warhammer 40000 through the Eye of Terror in the galactic relative west, where planets are warped to the whims of Chaos.
  • Age of Sigmar's Multiverse is larger and more like DnD's - The Realms are made out of the Winds of Magic, each corresponding to a Wind such as Fire, Life, Death or Shadow. Other planes exist and god-like beings can traverse the magical soup between the Realms, but mortals has to use Realmgates to move from Realm to Realm. The closer to the middle of a Realm one gets, the more normal it is (relative to our world); and the further away from the center one gets, the trippier it gets. Can you say infinite caves as sky and ground, air made out of brimstone and life turning to machines?