(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.

(optics) A surface to which rays reflected or refracted by another surface are tangents.

(physics) the effect on the surface of a liquid that makes it behave as a stretched elastic membrane; it is caused by unbalanced intermolecular forces / (physics) a measure of this effect

(of a missile) fired from an aircraft at a target on land or water

(of a missile) fired from the ground, or from a ship, at an aircraft in flight, or at an incoming missile

(idiomatic) To barely begin; to see or do only a fraction of what is possible.

capable of lowering the surface tension of a liquid

Overland flow of excess water (with or without accumulated contaminants) that cannot be absorbed by the ground as infiltration.

(geometry) A surface (in more than two dimensions, a plane is trivially developable) that can be flattened into a plane without distortion.