A fundamental property of sub-atomic elementary particles that means that behave as though they are spinning or rotating (although in reality they are not spinning at all). The concept has no direct analogue in the everyday world. Particles of spin ½ (e.g. electrons, positrons, neutrinos and quarks) make up all the matter in the universe, while particles with integer spin (0, 1 or 2) give rise to, or mediate, the forces operating between the matter particles (e.g. photons, gluons, W and Z bosons).