Most of J.R.R. Tolkien’s The Hobbit and The Lord of the Rings take place in Middle-earth.
Middle-earth is not the name of the entire universe in Tolkien’s mythology. It is a region of Arda, the world created in his legendarium. The stories include many locations within it, including the Shire, Rivendell, Mordor, Gondor, and Rohan.
The English term reflects the Old English middangeard and related Germanic ideas about the inhabited world. Tolkien’s use of the name therefore has a linguistic and mythological background rather than being a casual synonym for a fantasy land.
Other important locations lie outside Middle-earth. Aman, including Valinor, is across the sea in the West, while Númenor was an island kingdom that existed during an earlier period of the world’s history. These distinctions help explain why “Middle-earth” means a specific region, not every setting in Tolkien’s legendarium.