This document discusses conic sections, which are curves formed by the intersection of a plane and a cone. There are four types of conic sections: circles, ellipses, parabolas, and hyperbolas. Each conic section can be defined geometrically. For example, a circle is formed when the intersecting plane is perpendicular to the cone's axis of revolution. All conic sections can be represented by a second-degree equation, with some coefficient being non-zero to distinguish the different types of curves.