I am attempting to find a term for the opposite or the back side of a surface.
Typical terms for a: horizontal surface are top and bottom or "on top" and underneath, vertical surface are front and back, and for a nautical surface are windward and leeward.
Does anyone know if there is a proper term that would describe the opposite side of a flat surface, without regard to the surface's orientation or whether it is horizontally or vertically situated?
Maybe primary and secondary would work but there should be a better term.
I have attempted to find the newsgroups with the highest degree of relativity for this question, mainly knowledge in mechanical engineering and drafting, and I apologize if this is off topic for the newsgroup.
Thank you very much for your help.