J.R.R. Tolkien places Middle-earth at the center of The Lord of the Rings.
Middle-earth is the main inhabited region where the trilogy’s central events occur, including the Shire, Rivendell, Mordor, Gondor, and Rohan. The name translates Tolkien’s use of the Old English term middangeard, referring to the human world or inhabited world.
Middle-earth is not the name of the entire universe in Tolkien’s mythology. Arda is the world, while Middle-earth is one major region of it. Valinor lies in Aman, west of Middle-earth, and Beleriand belongs mainly to the earlier First Age stories.
The term also appears in The Hobbit and Tolkien’s other writings. Modern popular culture often uses “Middle-earth” for Tolkien’s whole setting, but the narrower geographical meaning is the most precise one.