In geometry, the curvature of a surface at a point is the value of the second derivative of the function describing the surface, at that point. Or, more comprehensibly, if a curve is described by f(x) (for all x), the curvature at (n, f(n)) is f''(n). This applies to shapes which aren't just curves, and to curves that aren't just defined a two-dimensioanl space.

Practical examples: The curvature of a straight line is 0, the curvature of a circle is a constant.

Compare with radius of curvature.