Define the following terms with respect to spherical mirrors:
(i) Pole
(ii) Centre of curvature
(iii) Principal axis
(iv) Principal focus

The middle point of the reflecting surface of a spherical mirror is called a pole. The letter P represents a pole.

Centre of curvature:

It is the centre of the sphere of a glass of which the mirror is a part. The letter C represents the centre of curvature.

Principal axis:

The principal axis of a spherical mirror is the straight line joining the centre of curvature and pole of the mirror.

Principal focus:

The mid-point of CP is called focus (F). It is the point on the principal axis of a spherical mirror where all incident rays parallel to the principal axis meet after reflection.

These points have been represented in the given diagrams.