J.R.R. Tolkien’s term “Middle-earth” translates from the Old English word middangeard.
Middangeard referred to the inhabited world, or the human world situated between cosmic realms. Tolkien also encountered related forms in Germanic languages, including Old Norse miðgarðr, which appears in the mythology of Midgard.
In Tolkien’s legendarium, Middle-earth is not the entire universe. It is the central inhabited region of Arda, the world created within his mythology. The term is therefore a translated name with a literary and historical background, not a reference to a planet shaped like a map between two places.
Tolkien’s use of the term reflects his interest in historical languages and mythic traditions. His invented world often gives familiar English names to concepts derived from older linguistic sources.