1.
A set of points whose total distance from two fixed points (the foci) is always the same.
2.
The longest diameter of the ellipse; it passes through both foci and the center.
3.
The shortest diameter of the ellipse; it is perpendicular to the major axis at the center.
4.
The midpoint of the major axis; the point exactly halfway between the two foci.
5.
The two endpoints of the major axis; the farthest points of the ellipse along its longest direction.
6.
The two endpoints of the minor axis; the farthest points of the ellipse along its shortest direction.
7.
Two fixed points inside the ellipse such that the sum of the distances to them from any point on the ellipse is constant.
8.
The distance from the center to either focus.
9.
Half of the major axis; the distance from the center to a vertex along the major axis.
10.
Half of the minor axis; the distance from the center to a co-vertex along the minor axis.
11.
A measure of how stretched the ellipse is.
