Meaning of focal distance in English:

focal distance

Pronunciation /ˈfəʊkl ˌdɪst(ə)ns/

noun

  • 1Optics
    The distance from a lens, lens system, or curved mirror to its focus along its focal axis.

  • 2Geometry
    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 of an ellipse or a hyperbola and its centre.

  • 3The distance between any given point of a parabola and its focus. In early use also: the distance between the focus of a parabola and its vertex.

Origin

Late 17th century; earliest use found in William Molyneux (1656–1698), experimental philosopher and constitutional writer. From focal + distance.