Realm is the name given to a dimension occupied by a single world.
The realms were created by the Elder Gods, who split the One Being through the use of the Kamidogu. Despite its separation, the One Being would subtly influence inhabitants of the realms to re-merge them back into its true form.
When in some of these realms, Raiden's powers weaken.
- Nightmare Realm
- Zaterra (was merged with Outworld)
- Vaeternus (was merged with Outworld)
- Hinpar (was presumably merged with Outworld)
- Rellim Ohcanep
- Thousands more realms (implied by Baron Reyland in Mortal Kombat: Conquest)