Name der dritten Ebene?

[Kas Ob.]

Very interesting question !,

If is up to me and with my bad English, ... i would use "Accumulational"....
My reason is:
Both Vertical and Horizontal are surfaces and they are perpendicular and they will represent full 3D and its 3 axes, so by adding one more (i mean a full flat surface) we need to go out of the 3D and start massing on the point itself, may be to represent point mass in both real and imaginary mass to represent a surface with 2 axes, where the mass can be positive and negative, similar to what jaenicke suggested about the "Deep", i even searched for "Depthal" word and seems there is no such thing in English.

Anyway here a very nice answers to the very same question:
https://english.stackexchange.com/qu...l-vertical-and

Distal sound fine.