of an Ellipse
Two fixed points on the interior of an ellipse used in the formal definition of the curve. An ellipse is defined
as follows: For two given points, the foci, an ellipse is the locus of points such that the sum of the distance to each focus is constant.
If the interior of an ellipse is a mirror, all rays of light
emitting from one focus reflect off the inside and pass through
of an ellipse, foci
of a hyperbola,
focus of a parabola, focal radius