In analogy with the

*conic**sections*, the set of points whose cartesian coordinates satisfy the general equation of the second degree, namely, :where A, B, C, F, G, H, J, K, L and M are real numbers and not all of A, B, C, F, G and H are zero is called a quadric surface. There are six types of non-degenerate quadric surfaces: The degenerate quadric surfaces are the empty set, a single point, a single line, a single plane, a pair of planes or a quadratic cylinder (a surface consisting of a non-degenerate*conic**section*in a plane and all the lines of ℝ 3 through that*conic*that are normal to ). Elliptic cones are sometimes considered to be degenerate quadric surfaces as well.