Surface has two meanings in Sorcery! Sorry about that! English is tricky.
Surface as a noun means "the top layer of a site," as in "the surface of a site." This is the more common usage of the word, which you can see on , , or .
Surface as a verb means "to move up from underwater," as in "surface the submerged minion." You can see examples of this on , , and .
Void squares do not have a surface (or subsurface).