Rilutaan: The Western Marches
There are many different planes of existence or dimensions that can be accessed as a part of the multiverse. Rilutaan occupies the Material Plane, often simply called "the world."
The other planes are listed below:
This is another matter entirely. The plane is an alternate dimension that functions differently than any of those listed above and is not accessible by any known means, magic or otherwise. It is a wholly alien place. It is sometimes called the Far Realm.