Arda is the invented world that contains much of J.R.R. Tolkien’s Middle-earth legendarium.
In Tolkien’s mythology, Arda is the world or realm shaped by the Valar under the authority of Eru Ilúvatar. Middle-earth is a major region of Arda, not the name of the entire cosmic setting. This distinction is one of the most common points of confusion in descriptions of Tolkien’s geography.
Arda includes places and regions connected with different periods of the legendarium, such as Middle-earth, Aman, Valinor, and the lost lands of earlier ages. Its history changes dramatically after major events including the destruction of Beleriand and the reshaping of the world.
The name Arda comes from Tolkien’s invented languages and is associated with the concept of the Earth or world. Tolkien’s mythology also places Arda within a larger cosmological framework involving Eä, the created universe, so Arda and Eä are related terms but are not interchangeable.