Specialized mathematical noun: the line or plane (polar) associated with a point relative to a conic or surface.
In projective geometry, the polar of a point with respect to a circle is the line perpendicular to the line joining the point to the circle's center.
En géométrie projective, la polaire d’un point par rapport à un cercle est la droite perpendiculaire à la droite joignant le point au centre du cercle.