There is another type of angular momentum, called spin angular momentum (more often shortened to spin), represented by the spin operator S = ( S x , S y , S z ) . Spin is often depicted as a particle literally spinning around an axis, but this is only a metaphor: the closest classical analog is based on wave circulation. All elementary particles have a characteristic spin (scalar bosons have zero spin). For example, electrons always have "spin 1/2" while photons always have "spin 1" (details below).