the distance from a lens, lens system, or curved mirror to its focus along its focal axis; = focal distance, n. 1.
Geometry. The distance between any given point of an ellipse or hyperbola and one of its foci. In early use also: the distance between the foci…
Mathematics power of a point n. (with regard to a circle or sphere) the square of the distance from a given point to the point of contact of a…
Geometry. In a skew surface, curveor line of striction: see quots.