Middle-earth is the fictional continent containing Mordor in J.R.R. Tolkien’s legendarium.
Mordor is a dark region in the southeastern part of Middle-earth, where Sauron established his stronghold and forged the One Ring. The term Middle-earth refers more broadly to the inhabited lands central to Tolkien’s mythology, including places such as the Shire, Gondor, Rohan and the Misty Mountains.
Tolkien adapted the name from the Old English middangeard and related Germanic expressions. It does not mean a planet called Earth in the modern scientific sense. Within Tolkien’s mythology, Middle-earth is part of Arda, the larger world created by Ilúvatar.
Readers sometimes use Middle-earth as a synonym for the entire Tolkien universe. That is broader than the term’s usual geographic meaning. Aman, for example, is a separate western land, while Beleriand belongs mainly to the earlier First Age narratives and was later destroyed or reshaped.