Arda is the name of the world that contains Middle-earth in J.R.R. Tolkien’s mythology. It is the realm created by Eru Ilúvatar and shaped through the events described in Tolkien’s legendarium.
Middle-earth is therefore not the name of the entire planet or world. It is one major region of Arda, alongside lands such as Aman and the historical regions of Beleriand. The term can be confusing because Tolkien’s maps and stories focus so heavily on Middle-earth that readers often use it as if it meant the whole setting.
Arda changes significantly across Tolkien’s imagined history. The world’s geography is altered by major events, including the destruction of Númenor and the reshaping of the seas. Tolkien also described Arda as belonging to the same world, or created universe, as our own distant mythic past.
The name comes from Tolkien’s invented languages and is related to his conception of the inhabited world. It provides the broadest geographical frame for the stories of the Elves, Men, Dwarves, and other peoples.