*The circle is the simplest and best known conic section. As a conic section, the circle is the intersection of a plane perpendicular to the cone's axis.
*An ellipse is all points found by keeping the sum of the distances from two points (each of which is called a focus of the ellipse) constant. The midpoint of the segment connecting the foci is the center of the ellipse. An ellipse can be formed by slicing a right circular cone with a plane traveling at an angle to the base of the cone.