what is ellipse
ellipse [(i-lips)] In geometry, a curve traced out by a point that is required to move so that the sum of its distances from two fixed points (called foci) remains constant. If the foci are identical with each other, the ellipse is a circle; if the two foci are distinct from each other, the ellipse looks like a squashed or elongated circle. Note: The orbits of the planets and of many comets are ellipses.