http://www.uesp.net/wiki/Lore:Nirn
Nirn is the planet on which the Elder Scrolls is set. It floats in the void of Oblivion and is, for all intents and purposes, the majority of the realm known as Mundus.[1] Sources often use the terms Nirn and Mundus synonymously, despite the technical differences in the two terms. Nirn was created during the Dawn Era by the Aedra and Anu-aligned spirits, based on Lorkhan's inspiration [2] and Magnus' designs.[3][4]
Tamriel is the main continent of Nirn and is its mythic and symbolic center. Tamriel is split into 9 provinces: Black Marsh, Cyrodiil, Elsweyr, Hammerfell, High Rock, Morrowind, Skyrim, Summerset Isle, and Valenwood.