Focal Length of a Parabola Definition
A curve symmetrical about the axes which is passing through the vertex and perpendicular to the directrix is called a parabola in a two-dimensional plane. In other words, we can say that the locus of points that are equidistant from both the directrix and the fixed point, say focus, is a parabola. The focal length of the parabola is the distance between the vertex and the focus along the axis of symmetry.