Most of J.R.R. Tolkien’s The Lord of the Rings takes place in Middle-earth. The term refers to the inhabited lands of Tolkien’s mythology during the periods covered by The Hobbit and The Lord of the Rings.
Middle-earth is not the name of the entire planet or universe in Tolkien’s mythology. It is a region of Arda, the world created within Tolkien’s legendarium. Other important regions include Aman, the Undying Lands, and Númenor, the island kingdom that existed in an earlier age.
The name comes from older Germanic and English expressions related to the inhabited world between heaven and the underworld. Tolkien’s Middle-earth therefore has both a literary and linguistic history. It is also commonly written with a hyphen, distinguishing it from ordinary descriptions of the middle of the Earth.