What are called centre of curvature and radius of curvature of mirror?

Centre of curvature: the centre of a spherical shell from which the mirror is made is called as the Centre of curvature of mirror. It is denoted by ‘C’.

Radius of curvature: the radius of a spherical shell from which the mirror is made is called as the radius of curvature of mirror. It is denoted by ‘R’.

The figure below shows the centre and radius of curvature of concave lens.