2. (Geom.)
(a) 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.
(b) 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.