A point p on a Regular Surface is said to be elliptic if the Gaussian Curvature or equivalently, the Principal Curvatures and have the same sign.
See also Anticlastic, Elliptic Fixed Point (Differential Equations), Elliptic Fixed Point (Map), Gaussian Curvature, Hyperbolic Point, Parabolic Point, Planar Point, Synclastic
Gray, A. Modern Differential Geometry of Curves and Surfaces. Boca Raton, FL: CRC Press, p. 280, 1993.