Elliptic point

A point on a regular surface at which the osculating paraboloid is an elliptic paraboloid. In an elliptic point the Dupin indicatrix is an ellipse, the Gaussian curvature of the surface is positive, the principal curvatures of the surface are of the same sign, and for the coefficients of the second fundamental form of the surface the inequality

$$LN-M^2>0$$

holds. In a neighbourhood of an elliptic point the surface is locally convex.