a) Curvature centre: This is the centre of a hollow glass sphere, of which a mirror is a component.

b) Curvature radius: This is the radius of the hollow glass sphere in which a mirror is contained.

c) Pole: The spherical mirror’s centre.

d) Principal axis: This is the straight line that runs from the spherical mirror’s pole to the centre of curvature.

e) Aperture: The part of a mirror where light is reflected.