(geography) Water collecting on the ground or in a stream, river, lake, sea or ocean, as opposed to groundwater.

(aeronautics) A moveable surface attached to a machine such as an aircraft or submarine that can be used to control the machine's motion in roll, pitch or yaw.

plural of control surface

(differential geometry) A unit vector at any given point P of a surface M which is perpendicular to the tangent plane T_P(M) of M at P. For a surface with parametrization ⃑x(u,v), it is given by

(mathematics) A surface formed when a given curve is revolved around a given axis. If the resulting surface is a closed one, it also defines a solid of revolution.

interfacial energy

(physics) An abstract boundary, of constant energy, useful for predicting the thermal, electrical, magnetic, and optical properties of metals, semimetals, and doped semiconductors.

plural of surface plasmon

(physics) The layer of molecules at the surface of a liquid that is responsible for surface tension / (ecology) The layer of surface water that forms a boundary between sea and air

Mail which is transported by motor vehicle, by railway, or by seacraft, but not by aircraft.