an ellipse is the locus of a point on a plane where the sum of the distances to two fixed points is a constant value. it can also be defined as the locus of a point where the ratio of the distance to a fixed point to the distance to a fixed straight line is a constant value less than 1. it is a type of conic section, which is the section line between a cone and a plane. the ellipse can be written in the equation as the standard formula x^2/a^2+y^2/b^2=1. it also has other expressions, such as parametric equation representation and so on. ellipses play an important role in kepler's three laws of planetary motion, which states that planetary orbits are ellipses with a star as the focus.