where 1=x = (x1, x2, ..., xD+1) is a row vector, xT is the transpose of x (a column vector), Q is a (D + 1) × (D + 1) matrix and P is a (D + 1)-dimensional row vector and R a scalar constant. The values Q, P and R are often taken to be over real numbers or complex numbers, but a quadric may be defined over any ring. In general, the ...

[n] - a curve or surface whose equation (in Cartesian coordinates) is of the second degree

• (n.) A quantic of the second degree. See Quantic. • (n.) A surface whose equation in three variables is of the second degree. Spheres, spheroids, ellipsoids, paraboloids, hyperboloids, also cones and cylinders with circular bases, are quadrics. • (a.) Of or pertaining to the second degree.

quadric surface noun a curve or surface whose equation (in Cartesian coordinates) is of the second degree
Found on https://www.encyclo.co.uk/local/20974

[projective geometry] There are generalizations of quadrics: quadratic sets. A quadratic set is a set of points of a projective plane/space, which bears the same geometric properties as a quadric: any line intersects a quadratic set in no or 1 or two lines or is containt in the set. ...