However, there is more to it than a simple definition. Udûn is also a place you can point to on the map of Middle-earth, although a place that is not mentioned by name in the prequel series.
While it’s not quite the same as Mordor, the volcanic region where Frodo and friends get the ring in the “Lord of the Rings” trilogy, it’s a specific location. in Mordor. Although not fully formal, Karen Wynn Fonstad’s book “Middle-earth map“a valuable resource nonetheless for fans of Tolkien’s works. Her map shows Udûn in northwestern Mordor, and also speculates that it is closely related to creation. to Mount Doom.
Given that we more or less only see saying that creation begins, it seems that Fonstad’s assertion is correct. It is likely that the Mount Doom eruption will signal a major change in the surrounding landscape, eventually turning parts of the beautiful Southlands into Mordor wasteland. Interestingly, however, the valley region adjacent to the volcano is not the only Udûn to appear in Tolkien’s writings.
https://www.slashfilm.com/1034097/the-rings-of-power-udun-explained/ The Rings of Strength: Udûn Explained