1. Pole of Mirror : The middle point of the reflecting surface is known as the pole of the mirror. It is situated on the face of the mirror and it is represented by P.
2. Centre of curvature : The centre of the spherical mirror, which is a portion of mirror is called centre of curvature. It is represented by C.
3. Radius of curvature: The reflecting surface of a spherical mirror which is a portion of sphere has radius R which is called radius of curvature. It is represented by R.
4. Principal axis: The line joining the pole and centre of curvature of the mirror is called Principal axis.
5. Normal: Line joining pole of the spherical mirrors and centre of curvature is perpendicular on it. Therefore any perpendicular line of the spherical mirrors is equal to its centre of curvature.
6. Focus Length : Length of the pole of the spherical mirror to the main focus is known as Focus length. It is represented by f.
