In geometry, Wallis's conical edge is a ruled surface given by the parametric equations x = v cos ⁡ u, y = v sin ⁡ u, z = c a 2 − b 2 cos 2 ⁡ u {\displaystyle x=v\cos u,\quad y=v\sin u,\quad z=c{\sqrt {a^{2}-b^{2}\cos ^{2}u}}} where a, b and c are constants. Wikipedia