Line of symmetry
A line of symmetry is a line that divides a figure into two congruent parts. In the figure below, the lines of symmetry divide the figures into mirror images.
Some figures have more than one line of symmetry. In the figure below, all the lines of symmetry for the equilateral and square are shown. For the circle, only four of an infinite number of lines of symmetry are shown.
See also symmetry.