An ellipse is a geometric shape that looks like a stretched circle. It is defined as the set of points where the sum of the distances from two fixed points, called foci, is constant. Ellipses can be found in various contexts, such as in the orbits of planets around the Sun. In mathematics, the standard equation of an ellipse centered at the origin is (x^2/a^2) + (y^2/b^2) = 1, where a and b are the lengths of the semi-major and semi-minor axes, respectively. Ellipses are also used in physics, engineering, and astronomy to describe paths and shapes.