Definition of focal property in English:

focal property

noun

Geometry
  • 1The property that the lines though any point of an ellipse or hyperbola and its foci make equal angles with the tangent at that point.

  • 2The property that the line though any point on a parabola and its focus and the line that is parallel to the axis and runs through the same point make equal angles with the tangent at that point.

Origin

Early 19th century; earliest use found in John Mason Good (1764–1827), physician and surgeon.