What does directrix mean?
A straight line in a parabola or other curve, to which any point on the curve is perpendicular. In optics, the directrix of a mirror or lens is an imaginary line that is perpendicular to the principal axis and to which the reflected or refracted rays converge.
Example
"The directrix of the parabola was used to calculate the focal length of the mirror."
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.