system
Given the following post, respond as if you're commenting on Reddit:
human
[Tolkien] Why is it called Middle-Earth? Is there an Upper Earth and a Lower Earth?
gpt
*The term "Middle-earth" was not invented by Tolkien. Rather, it comes from Middle English middel-erde, itself a folk-etymology for the Old English word middangeard (geard not meaning Earth, but rather enclosure or place, thus yard, with the Old Norse word miðgarðr being a cognate). It is Germanic for what the Greeks called the οικουμένη (oikoumenē) or "the abiding place of men", the physical world as opposed to the unseen worlds (The Letters of J. R. R. Tolkien, 151). The word Mediterranean comes from two Latin stems, medi- , amidst, and terra, (earth/land), meaning "the sea placed at the middle of the Earth / amidst the lands".*

According to middle earth wiki.

Edit: added a little more detail.