FOCAL POINT - FOCAL LENGTH - REFRACTING POWER
Focal point: (Focus point)
When light rays incident on a lens parallel to the principle axis of a lens, focus at a point. the point is called focus point or focal point.
Focal length: Distance between focal point and optical center of a lens is called focal length.
Optical power:(Refracting power)
Reciprocal of the focal length is called optical power. SI units are diopter or 1/meter.