Symmetry operation
OPERATIONS IN MOLECULAR SYMMETRY WHERE THE INITIAL DISPLACEMENTS OF THE ATOMS ARE UNCHANGED
Improper axis of rotation
In group theory, geometry, representation theory and molecular symmetry, a symmetry operation is a transformation of an object that leaves an object looking the same after it has been carried out. For example, as transformations of an object in space, rotations, reflections and inversions are all symmetry operations.