Focus of a Parabola

The focus of a parabola is a fixed point on the interior of a parabola used in the formal definition of the curve.

A parabola is defined as follows: For a given point, called the focus, and a given line not through the focus, called the directrix, a parabola is the locus of points such that the distance to the focus equals the distance to the directrix.

Note: For a parabolic mirror, all rays of light emitting from the focus reflect off the parabola and travel parallel to each other (parallel to the axis of symmetry as well).

See also

Conic sections, foci of an ellipse, foci of a hyperbola, focal radius