subterranean humanoids; mole people
Used in science fiction, fantasy, and conspiracy theories to refer to human-like beings living underground.
In that novel, subterranean humanoids have built an advanced civilization at the center of the Earth.
There is an urban legend that mole people live in the subway tunnels.
Compound of 地底 (chitei, 'underground depths') and 人 (jin, 'person'). The term is a modern coinage for fictional subterranean humanoids.