In geometry, a shape that has the greatest number of lines of symmetry is a circle. A circle has an infinite number of lines of symmetry because you can draw symmetry lines through the center and any point on the circumference, and they will all divide the circle into two equal halves.
If you're considering polygons, regular polygons have a large number of lines of symmetry based on the number of their sides. For example, a regular hexagon has 6 lines of symmetry, while a regular octagon has 8 lines of symmetry. However, none of these can match the infinite symmetry of a circle.