What is Middle-earth?
Middle-earth, also known as Ennor or Endor, is the main continent of Arda, Tolkien's imagined version of our Earth's past. Middle-earth is reminiscent of old Europe in the Middle Ages and earlier—with a significant difference. This version of our world is populated not just by humans but also by Elves, Hobbits, Orcs, and Dwarves, among many species.
According to the mythology of Tolkien's Middle-earth, the world of Arda used to consist of interconnected worlds. At the center of that universe was Middle-earth, the world of humans, and across the great ocean, Belegaer, was Aman. There are other lands in Arda, but these are the two main continents.