conic section

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The intersection of a right circular cone and a plane, which generates one of a group of plane curves, including the circle, ellipse, hyperbola, and parabola.
• noun A graph of the general quadratic equation in two variables.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geometry Any of the four distinct shapes that are the intersections of a cone with a plane, namely the circle, ellipse, parabola and hyperbola.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (geometry) a curve generated by the intersection of a plane and a circular cone