When the Gaussian curvature 
is everywhere negative, a surface is called anticlastic and is saddle-shaped. A surface on which 
is everywhere positive is called
synclastic. A point at which the Gaussian
curvature is negative is called a hyperbolic
point.
Anticlastic
See also
Elliptic Point, Gaussian Quadrature, Hyperbolic Point, Parabolic Point, Planar Point, SynclasticExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Anticlastic." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Anticlastic.html