In mathematics, a
discrete symmetry is a symmetry that describes non-continuous changes in a system. For example, a square possesses discrete
rotational symmetry, as only rotations by multiples of right angles will preserve the square's original appearance. Discrete symmetries sometimes involve some type of 'swapping', these swaps usually being called
reflections or
interchanges. In mathematics and
theoretical physics, a
discrete symmetry is a
symmetry under the transformations of a
discrete group—e.g. a
topological group with a
discrete topology whose elements form a finite or a
countable set.