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)
The locus of the intersections of the tangents at the end of chords of an ellipse which pass through a common point is a straight line.
A bit of a mouthful, but play with the diagram and it will become clear.