A conic is the curve obtained as the intersection of a plane with the surface of a double cone (a cone with two nappes). Planes that pass through the vertex of the cone will intersect the cone in a point, a line or a pair of intersecting lines. These are called degenerate conics.[br]The circle is obtained when the cutting plane is parallel to the plane of the generating circle of the cone. [br]If the cutting plane is parallel to exactly one generating line of the cone, then the conic is unbounded and is called a parabola. [br]In the remaining case, the figure is a hyperbola: the plane intersects both halves of the cone, producing two separate unbounded curves.