Question

what is pole ,centre of curvature

Answer 1

Pole is the central part of one side of the mirror.

Centre of curvature is the central part of the mirror.It is like radius of sphere.

Answer 2

It is the center of the reflecting surface of the concave mirror also called vertex of mirror, generally denoted by letter ‘P’.

Center of curvature: 
It is the center of that sphere of which the concave mirror forms a part, denoted by letter ‘C’