The outer or the topmost boundary of an object. A material layer constituting such a boundary. Mathematics The boundary of a three-dimensional figure. Mathematics The two-dimensional locus of points located in three-dimensional space. Mathematics A portion of space having length and breadth but no thickness. The superficial or external aspect: "a flamboyant, powerful confidence man who lives entirely on the surface of experience\u201d ( Frank Conroy). An airfoil. Relating to, on, or at a surface: surface algae in the water. Relating to or occurring on or near the surface of the earth. Superficial. Apparent as opposed to real. To provide with a surface or apply a surface to: surface a table with walnut; surface a road with asphalt. To rise to the surface. To emerge after concealment. To work or dig a mine at or near the surface of the ground. on the surface To all intents and purposes; to all outward appearances: a soldier who, on the surface, appeared brave and patriotic.