Vector which is perpendicular to said surface or manifold. In a inner product space, the inner product of the normal vector with all vectors which comprise the surface is 0.
... (+ 1942)
March 7 - Reinhard Heydrich, Nazi official
March 20 - B. F. Skinner, behavioral psychologist (+ 1990)
March 23 - Joan Crawford, actress
March 26 - Joseph ...