Line of Symmetry

The dashed line is called the ‘line of symmetry’. If you fold the figure in half around the dashed line, and the two halves match exactly, the figure is then symmetric.

A figure that cannot be folded around an imaginary line with the two halves matching exactly is not symmetric. It does not have a line of symmetry. Here is an example:

You cannot fold this figure in half and have both halves match exactly.