From Citizendium, the Citizens' Compendium
- : A curve obtained as the intersection of a plane with a circular cone; also called second order curve because of its algebraic representation.
- : A planar curve defined by a quadratic equation: ax2 + bxy + cy2 + dx + ey + f = 0 in the affine plane, or in the projective plane; also called a conic because of its geometrical generation.
- Parabola : The planar curve formed by the points that lie as far from a given line (the directrix) as from a given point (the focus).
- : Planar curve formed by the points for which the difference of the distances to two given points is a given number.