the circle that touches a curve (on the concave side) and whose radius is the radius of curvature

the rate of change (at a point) of the angle between a curve and a tangent to the curve

the property possessed by the curving of a line or surface

ellipse in which the two axes are of equal length; a plane curve generated by one point moving at a constant distance from a fixed point

an unofficial association of people or groups

travel around something

movement once around a course