File:Normal_vectors2.svg · Wikimedia Commons · See Wikimedia Commons
normal
Sign in to savein geometry, an object that is perpendicular to a given object, vector perpendicular to a curve or surface
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Encyclopedic overview
A polygon and its two normal vectors A normal to a surface at a point is the same as a normal to the tangent plane to the surface at the same point. Tangent and normal to a curve in a Cartesian coordinate system.
In geometry, a normal is an object (e.g. a line, ray, or vector) that is perpendicular to a given object. For example, the normal line to a plane curve at a given point is the infinite straight line perpendicular to the tangent line to the curve at the point.
Excerpted from Wikipedia’s “normal” article, available under the CC BY-SA 4.0 licence.