The fictional land where much of J.R.R. Tolkien’s legendarium takes place is Middle-earth.
Middle-earth is the setting for The Hobbit and The Lord of the Rings, as well as many stories later collected in The Silmarillion. It is a region of Arda, Tolkien’s broader imagined world, and contains places such as the Shire, Gondor, Mordor, Rohan, and Mirkwood.
The term is Tolkien’s English rendering of a concept related to the Old English word middangeard and similar expressions in Germanic languages. It does not mean a planet separate from Earth in Tolkien’s conception; his mythology presents it as an imagined ancient phase of our own world.
Readers sometimes use “Middle-earth” to mean the entire Tolkien universe. More precisely, Valinor and other lands west of the sea are also part of Arda, while Middle-earth is the major eastern region where most of the familiar narratives occur.