> The 4-tier naming is honestly as clear as you can get. I have no idea what people are so confused about.

I wouldn't necessarily say that. Atmospheric mass may be obvious to us, but I suspect it's not nearly as universal knowledge as one may assume.

And I actually assumed at first that they were based on distance from us (terra < luna < sol), so I kept confusing terra and luna.

It’s totally clear. About as clear as mud.