An included side is one that links two angles together. It can be said it is a line 'included' between two angles. A non-included side take two consecutive angles and move on to the next sides in either direction.
Considering a polygon, for two polygons to be congruent, they must have an equal number of side-angle for n sides and n angles. A non-included side of a polygon shares a side with only one <u>angle</u> of a pair of angles.
