Nor″mal (nôr″mal), n. [Cf. F. normale, ligne normale. See Normal, a.] 1. (Geom.) Any perpendicular.
2. (Geom.) A straight line or plane drawn from any point of a curve or surface so as to be perpendicular to the curve or surface at that point.
☞ The term normal is also used to denote the distance along the normal line from the curve to the axis of abscissas or to the center of curvature.