Back focal distance, meaning the distance from the tip of the lens' furthest rear surface to the film/image sensor surface where the image is focused. Read articles that include this term

The distance between the image plane and the rear most portion of the lens.

Cameras are focused by moving the image sensor in relationship with the lens, which enables differing back focal lengths for the lens.  This adjustment is called Back Focus and is important when fitting a zoom.

A term for when the part in focus is not the subject, but the area behind the subject. The term "back focusing" is often used to describe mistakes where the background is in focus instead of the intended subject.

Back focus is a term used to describe the relationship of the distance of the lens to the image device. This distance is critical to maintain the proper depth of field through changing focal lengths a [..]

Back focal distance, meaning the distance from the tip of the lens' furthest rear surface to the film/image sensor surface where the image is focused. Read articles that include this term

A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different back focal lengths of lenses. An important adjustment when a zoom lens is fitted.

distance between the back surface of the lens and the image plane