Quadric (projective Geometry)
In projective geometry a quadric is the set of points of a projective space where a certain quadratic form on the homogeneous coordinates becomes zero. It may also be defined as the set of all points that lie on their dual hyperplanes, under some projective duality of the space.
Read more about Quadric (projective Geometry): Formal Definition, Matrix Representation, Polarity, Tangent Hyperplane, and Singular Points, Intersection of Lines With Quadrics