> A conoid is a ruled surface whose rulings are parallel to a plane (called the directrix plane) and intersect a fixed line (called the axis of the conoid) (Gel

> A conoid is a ruled surface whose rulings are parallel to a plane (called the directrix plane) and intersect a fixed line (called the axis of the conoid) (Gellert et al. 1989, p. 202). Examples include the circular conoid, helicoid, hyperbolic paraboloid, parabolic conoid, Plücker conoid, right circular conoid, Wallis's conical edge, Whitney umbrella, and Zindler conoid. If the axis is perpendicular to the directrix plane, the conoid is called a right conoid (Gray et al. 2006, p. 436). https://mathworld.wolfram.com/Conoid.html https://mathworld.wolfram.com/Conoid.html