Cone, in geometry, is a solid figure whose base lies on a plane and is bounded by a closed curve called the directrix. The lateral surface (side) of the cone consists of all the line segments connecting points of the directrix to the cone's vertex, a fixed point not on the plane of the base. When the directrix is a circle, the cone is a circular cone. If the line segment from the vertex to the center of the circle is perpendicular to the plane of the base, the cone is a right circular cone. When a right circular cone is intersected by a plane that does not contain the vertex, a curve called a conic section is formed. Circles, ellipses, hyperbolas, and parabolas are conic sections.