Eldritch appears to have a couple of meanings:
The first is it can refer to the entire world KQ7 takes place in (Realm of Eldritch).
Secondly, it appears to refer to the combined lands of Ooga Booga, The Desert, Vulcanix Underground, Falderal (and Nonsense Land), the Swamp, the Were-Woods, and the Bountiful Woods and possibly Etheria and Cloudland above (but not Dreamland).
The third meaning appears to be the name for the lower lands, but only those surrounding the Volcano.
It is unknown if there are any lands outside of those lands. But its believed the volcano is capable of destroying the entire world.
At least two of the lands are kingdoms in their own rights. These include Troll Underground (aka Vulcanix Underground), and Ooga Booga Land (aka Ooga Booga). Nonsense Land and Falderal appears to be a duchy, and the Desert has no government. Etheria is also considered a kingdom.