Middle-earth is the fictional world containing Mordor, Gondor, and Rohan in J.R.R. Tolkien’s writings.
The name refers to the central inhabited region of Tolkien’s imagined mythology, especially the setting of The Hobbit and The Lord of the Rings. Mordor is Sauron’s realm, Gondor is a major human kingdom, and Rohan is the horse-lord kingdom whose riders are known as the Rohirrim.
Middle-earth is not the whole of Tolkien’s universe. It is part of Arda, the broader world created in Tolkien’s mythology. Other regions, such as Valinor, lie elsewhere in that world, while Beleriand belongs mainly to the geography of the First Age.
The term is sometimes mistakenly used as a synonym for every Tolkien location. Númenor, for example, is an island kingdom that existed chiefly in the Second Age. Tolkien adapted the name from the older Germanic idea of a central world between other realms.