There is no such expression. The normal to a surface, at a given point is the radius of curvature of the surface, at that point.
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The pleura is a membrane that surrounds the lungs of mammals. Presumably, the phrase means that the surface of the pleura was found to be normal in an examination.
The normal vector to the surface is a radius at the point of interest.
A curved surface area can be described as one where the gradient of the normal to the surface changes smoothly from point to point.
Bar is a unit used to measure pressure, one bar is the normal atmospheric pressure of the on the surface of the earth, and ten bar is when the pressure is ten times the normal atmospheric pressure on the surface of the earth.
The angle between the light ray and the normal (perpendicular) to the surface at the point of reflection.