A line along a normal vector (i.e., perpendicular to some tangent line).

If is a centrosymmetric set which has a twice differentiable boundary, then there are normals through the center (Croft et al. 1991, p. 15).

Croft, H. T.; Falconer, K. J.; and Guy, R. K. Unsolved Problems in Geometry. New York: Springer-Verlag, 1991.

CITE THIS AS:

Weisstein, Eric W. "Normal Line." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/NormalLine.html