In
mathematics, an
ellipse is a
curve on a plane that surrounds two
focal points such that the sum of the distances to the two focal points is constant for every point on the curve. As such, it is a generalization of a circle, which is a special type of an ellipse that has both focal points at the same location. The shape of an ellipse (how 'elongated' it is) is represented by its
eccentricity, which for an ellipse can be any number from 0 (the
limiting case of a
circle) to arbitrarily close to but less than 1.