Quote Originally Posted by Maat Mons View Post
At least, I think some of those uses of "surface" were meant to refer to an object's exterior, not a 2D space.
Surface in the same sense as a circle is a "surface" of a disc. In mathematical terms,
a disc: x^2 + y^2 <= r^2
a circle: x^2 + y^2 = r^2