1. Pole of the mirror : pole of the mirror is the center of the reflecting surface. The ray of light along the principal axis which is incident on the pole of the mirror retraces its path along the principal axis. 

2. Principal focus : It is the point of convergence of a parallels beam of light which are also parallel to principal after reflection. It is denoted by ‘F’. 

3. Focal length : The distance between the pole of the mirror and the point of focus reflected parallel rays of light which are incident on the mirror is called focal length. It is denoted by ‘P’. 

4. Center of curvature : It is center of the sphere of which the mirror is a part. It is denoted by ‘C’. 

5. Radius of curvature : The radius of the sphere of which the mirror apart is called radius of curvature it is denoted by ‘V’. the radius of curvature is twice the focal length r = 2 ‘f’ 

6. Principal axis : The imaginary extended line on which the pole of the mirror, the point of focus and the center of the curvature are located is called principle axis. 

7. Object distance : The distance of the object from the pole of the mirror is called object distance it is denoted by ‘V’. 

8. Image distance : The distance between the mirror and the image is called image distance it is denoted by ‘V’.