Curvature
cur·va·ture
/ˈkərvəCHər,ˈkərvəˌCHo͝or/
noun
1 : the act of curving : the state of being curved.
2 : a measure or amount of curving specifically : the rate of change of the angle through which the tangent to a curve turns in moving along the curve and which for a circle is equal to the reciprocal of the radius.