The document discusses the key elements that define an ellipse: - The ellipse has a center point O. - It has a major axis A1A2 of length 2a and a minor axis B1B2 of length 2b. - There are two focal points, F1 and F2, located a distance c from the center. - The sum of the distances from any point on the ellipse to the two focal points is a constant, equal to 2a.