+In geometry, a **normal line** is a line or vector that is perpendicular to a [Tangent Line](/wiki/tangent_line) at a given point on a curve or surface. It points in the direction of steepest change, often defining the orientation of a [Surface Normals](/wiki/surface_normals).
+## See also
+- [Perpendicular](/wiki/perpendicular)
+- [Gradient](/wiki/gradient)
+- [Curve](/wiki/curve)
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