What Are Lines of Symmetry?

Lines of symmetry show how shapes can be flipped

If shapes have any reflectional symmetry, they'll have at least one line of symmetry. Lines of symmetry are the lines that you could flip a shape over and have the shape look exactly the same.

For example, squares have four lines of symmetry—one bisecting each set of parallel sides, and one bisecting each set of opposite corners (on the diagonals). If you flipped the square around any of the colored lines in the image below, it would look exactly the same.