a) Pole : The centre of the spherical mirror is called pole of the mirror.
b) Centre of curvature : The normal from a concave mirror converge at a point, that point is called centre of curvature.
c) Focus : The rays coming from distinct object parallel to concave mirror will converge at a point called focus or focal point.
d) Radius of curvature : The distance between vertex and centre of curvature is called radius of curvature.
e) Focal length : The distance between vertex and focus.
f) Principal axis : The horizontal line which passes through the centre of curvature.
g) Object distance : The distance between object and mirror is called object distance.
h) Image distance : The distance between image and mirror is called image distance.
i) Magnification : Ratio of size of image to size of object.