Parabola With Focus and Directrix
Illustration of a parabola - a curve which is the locus of a point that moves in a plane so that its distance from a fixed point (focus) in the plane is always equal to its distance from a fixed line (directrix) in the plane.
GalleriesConic Sections: Parabolas
G.A. Wentworth Plane And Solid Geometry (Boston: Ginn & Company, 1899) 410