Elementos of a mirror: Place the mouse on the corresponding element and you will be able to see what is known as: the optical axis, the centre of curvature and the focal point of a mirror.

centre of curvature: is the centre of the imaginary sphere constituted by the mirror.
optical axis: the horizontal line that goes through the centre of curvature.
focal point: the point on the optic axis through which the reflected parallel rays pass. It is situated midway on the line joining the centre to the mirror.