A Circle is an Ellipse, where both foci are at the same point .In other words, a circle is a "special case" of an ellipse .An ellipse is the set of all points on a plane whose distance from two fixed points F and G add up to a constant. In an ellipse, there are two radius measures, one horizontally along the x-axis, the other vertically along the y-axis.For a circle both these have the same value.
The statements true for an Ellipse are:
An ellipse is similar to a circle.
An ellipse has two foci.
The sum of the distances from each focus to any point on the ellipse will always be the same.