Plane

A plane, also known as a dimension, is a large pseudo-geographic designation in the Warcraft universe. Some adventurers go beyond Azeroth to other planes of existence. It is there that they encounter eternals and demons, adventurers and villains, strange and vastly powerful creatures, and conflicts that span worlds — if not the universe itself.

There is something greater than the physical world of Azeroth. It lies infinitely far away, yet also infinitesimally close. It has places of brilliant purity and the darkest chaos. Creatures of air, fire, and shadow call these places their homes; and those from Azeroth who dare to travel into these realms will find them unlike anything they have ever seen before.

History
They are the planes, and the physical world of Azeroth is but one of them. Though the titans and eternals have known about the planes for longer than the recorded history of the world, the first time mortal creatures on Azeroth suspected there was something other than the world around them was when the Kaldorei made their way out of the jungles to the shores of the Well of Eternity and stared deep into its waters. There they sensed a great power, and in a course of events that would change the world forever, dedicated themselves to its study. They hoped that they would discover the moon goddess Elune within its waters, but instead they plumbed the darkness and felt the cold touch of the Burning Legion waiting on another plane, the Twisting Nether.

Multiverse
The multiverse is the term for all the planes of the universe put together. The multiverse is the universe. Malygos studies the various planes of the multiverse both remotely and in person.

It is said that Al'Akir is aware of all air spells that are cast anywhere throughout the multiverse, although if this is true, he rarely becomes personally involved in their resolution unless they affect him directly.

Material Plane
The Material Plane, also known as mortal plane(s), mortal world(s), material world(s) or physical world(s), encompasses the planets, moons, and suns. This includes planets such as Azeroth, and included such planets as Draenor. All material worlds are made from the same planar material as the known material worlds, though some of them might possess different basic planar traits (from basic physical traits to magic traits).

Each of these worlds, though they share most of the same planar traits, is separated from the rest in its particular material pocket. As such, each world is treated as its own separate plane — spells such as "teleport" that allow for transport within the Material Plane do not allow for transport between isolated material pockets. Another plane, the Twisting Nether, must be traversed to journey from one to another.

The eternals and even the goddess Elune share residence on the Material Plane of Azeroth with mortal beings.

Elemental Plane
The Elemental Plane is the home of all elementals that were removed from Azeroth by the Titans millenias ago.

Emerald Dream
The Emerald Dream is a kind of echo of what Azeroth would be like if intelligent beings had not altered its surface.

Twisting Nether
The Twisting Nether is the astral plane between worlds.

Non-existant planes
The Warcraft universe is both simple and vast, it has no distinct Astral, Ethereal, Inner, Outer, Positive, or Negative Planes — just a measureless nothing known as the Great Dark Beyond. However, although those planes doesn't exist, they have a counterpart or are somehow related to the Warcraft universe.

Astral Plane
The Astral Plane does not exist in Warcraft universe, it is replaced by the Twisting Nether. Outland exists in this plane.

Ethereal Plane
There is no Ethereal Plan in the Warcraft universe. No exact equivalent of the Ethereal Plane exists in the Warcraft universe. Only the Emerald Dream can be clearly mapped to another plane, that of the physical world of Azeroth, yet they remain distinct places in the cosmos and grow more disparate with each change made in the mortal realm. Ethereal Spells result in the target becoming invisible and intangible to all creatures and effects on the Material Plane.

As such, any creature described as existing or otherwise interacting with the Ethereal Plane is treated as simply being incorporeal on the Material Plane, but are considered invisible.

Inner and Outer Planes
Only the titans remain as creatures who may originate from a place beyond the known planes, and the dwarves have yet to discover the answer to their mystery.

The final destination of the spirits of the deceased remains a mystery to the priests and philosophers of Azeroth. However, as spells such as resurrection can reunite a dead body with its spirit, and a majority of living creatures from the tauren to the troll shadow hunters claim they can communicate with and call upon the power of the spirits, a widely held belief is that the spirits of the dead remain on the Material Plane — in an immaterial state that can only be altered or contacted through the use of magic.

Positive Energy Plane, Negative Energy Plane, and Shadow Plane
These planes doesn't appear to exisist. But their forces are known to flow through Azeroth and the Twisting Nether. These forces are not limited to any single plane; they are instead an integral part of every aspect of the Warcraft universe, woven into every plane. Thus, spells that call upon these energies such as harm, heal and shadow conjuration instead draw upon local sources rather than reaching to another plane.

Positive energy remains associated with the energies possessed by living beings, and negative energy with the motive forces of death and the undead. Thus, spells that aid the living with positive energy will harm the undead, and spells that would injure the living using negative energy will heal the undead.

Magical weapons that have effects wielding these energies draw upon that positive or negative energy bound into their own material, freed by enchantment.

The Shadow Plane may be the Realm of Shadows, though it is never specified.

Realm of Shadows
The Realm of Shadows, also known as Shadow Realm or Shadow Plane, is a dimension apparently accessible by powerful death knights such as Lady Alistra and Salanar the Horseman, who can teleport others (and probably themselves) to and from it. It appears as a shadowy version of the real world. Salanar the Horseman's dark riders kills captured horses and raises them as Acherus Deathchargers there, and death knight initiates must then venture into the realm to defeat the horsemen and take the deathchargers for themselves, a task in which few of the initiates succeed. Shadowy Tormentors inhabit this dimension. This may be the same as the world of shadows that becomes visible when an Elixir of Shadows is drunk. It may also have something to do with shadow magic and shades.

The Great Dark Beyond
The Great Dark Beyond is the place where all the planets lay in the Warcraft universe. But a philosophical placeholder was agreed that beyound the boundaries of the Twisting Nether, the Great Dark could become its own plane.

Other planes

 * Twilight Realm
 * Titanic Armory: A group of heroes discovered a small portal in the Nether. The portal lead to a demiplane full of titan artifacts — weapons the Pantheon deemed too destructive to use.

Higher planes
According the Warcraft RPG, when the term "higher plane" is used, it is in reference to one of the Known Planes, such as the Emerald Dream, the Twisting Nether, the Great Dark Beyond, the Elemental Plane, or simply another planet out in the Great Dark Beyond. There are scholars who study the concept of planes and wonder if there are more to discover.

According to the books, there are no Dungeons & Dragons style planes within the Warcraft universe. The Warcraft universe is both simple and vast. Unlike the standard D&D world, Azeroth has no distinct Astral, Ethereal, Inner, Outer, Positive, or Negative Planes — just a measureless nothing known as the Great Dark Beyond. An infinite number of worlds spin within the multiverse and its impossible to say whether they are scattered across the universe or superimposed upon each other.

Granted its also said that nether drakes are able to shift between the Astral and Physical Planes according to the World of Warcraft lore writers. However, it has been confirmed that the Astral Plane is yet another alternate term for the Twisting Nether.