Here are the definitions for each type:[br][list][*][color=#0000ff]Positive Curvature:[/color][color=#38761d] A surface has positive curvature [/color][i][color=#93c47d]at a point[/color][/i][color=#38761d] if the surface curves away from that point in the same direction relative to the tangent to the surface, regardless of the cutting plane. Alternatively, the surface stays on one side of the tangent plane at that point. [/color](Thus the top of your head, the end of your finger, or the inside of your armpit are points of positive curvature.)[/*][/list][list][*][color=#0000ff]Negative Curvature: [/color][color=#38761d]A surface has negative curvature [/color][i][color=#93c47d]at a point[/color][/i][color=#38761d] if the surface curves away from the tangent plane in two different directions. [/color](The classic example is a saddle, which can be found on your body in the space between your thumb and forefinger, or along the inside of your neck.)[/*][/list][list][*][color=#0000ff]Zero Curvature:[/color][color=#38761d] A flat and infinite 2D plane[/color][/*][/list]