|focal length or focal distance|
|the distance from the focal point of a lens or mirror to the reflecting surface of the mirror or the centre point of the lens|
|focal distance or focal distance|
focal length n.
The distance from the surface of a lens or mirror to its focal point. Also called focal distance, focus.
|focal length (fō'kəl) Pronunciation Key
The distance between the optical center of a lens or mirror to its focal point.