Recently students flipped through magazines looking for images that included lines of symmetry. Once an image was selected they cut along the line of symmetry and drew the missinng half. Not all of the images they selected are true defintions of symmetry but I believe that came away with a better understanding of how to identify symmetry.
Merriam Webster defines SYMMETRY as:
the property of being symmetrical; especially : correspondence in size, shape, and relative position of parts on opposite sides of a dividing line or median plane or about a center or axis
