A square has 4 lines of symmetry. These lines of symmetry are:

1. A vertical line through the center (dividing the square into two equal left and right halves).
2. A horizontal line through the center (dividing the square into two equal top and bottom halves).
3. A diagonal line from the top-left corner to the bottom-right corner.
4. A diagonal line from the top-right corner to the bottom-left corner.

Each line of symmetry divides the square into two mirror-image halves.