Final answer:
An ellipse is a curve in which the sum of the distances from any point on the curve to two fixed points called foci is constant.
Step-by-step explanation:
An ellipse is defined as an open or closed curve in which the sum of the distances from any point on the curve to two fixed points called foci is constant. The equation of an ellipse can be found using the formula:
(x-h)^2/a^2 + (y-k)^2/b^2 = 1,
where (h, k) represents the coordinates of the center of the ellipse, and a and b are the lengths of the semi-major and semi-minor axes, respectively.