One definition of an ellipse is as the locus of points the sum of whose distance from two fixed points (the foci) is constant.
This gives you a way to draw the ellipse with two pins and a piece of string.
Here we relate that definition to the focal property: that light emanating from one focus reflects to the other focus.
This app allows you to experiment with an alternate construction of an ellipse. The tracing of the perpendicular bisector of the segment between a point on a circle and a point in the circle create an elliptical locus. (G-GPE 3)
The polar point of a line in an ellipse is a common point to the chords defined by the common tangents through the points on the line.
Play with it and the meaning will be clear!
(Go to Full Screen if the green points won't drag)