- a curve formed by the intersection of a plane with a right circular cone; an ellipse, a circle, a parabola, or a hyperbola.
- one of a group of curves formed by the intersection of a plane and a right circular cone. It is either a circle, ellipse, parabola, or hyperbola, depending on the eccentricity, e, which is constant for a particular curve e = 0 for a circle; e <1 for an ellipse; e = 1 for a parabola; e>1 for a hyperbola
