Conic section (Geom.), a curved line formed by the intersection of the surface of a right cone and a plane. The conic sections are the parabola, ellipse, and hyperbola. The right lines and the circle which result from certain positions of the plane are sometimes, though not generally included. -- Conic sections, that branch of geometry which treats of the parabola, ellipse, and hyperbola. -- Conical pendulum. See Pendulum. -- Conical projection, a method of delineating the surface of a sphere upon a plane surface as if projected upon the surface of a cone; -- much used by makers of maps in Europe. -- Conical surface (Geom.), a surface described by a right line moving along any curve and always passing through a fixed point that is not in the plane of that curve.