Definitions for "Directrix"
A line along which a point in another line moves, or which in any way governs the motion of the point and determines the position of the curve generated by it; the line along which the generatrix moves in generating a surface.
A straight line so situated with respect to a conic section that the distance of any point of the curve from it has a constant ratio to the distance of the same point from the focus.
(n) A line (typically curved) that describes the path of a straight line (the generatrix). The path of the generatrix along the directrix describes ruled surfaces or solids.
Keywords:  directress
A directress.