Can anyone explain the physical meaning of "spin" in QM? I'm a physics master student and i've completed several quantum mechanics (or related) courses and i have no problem working with Pauli spin matrices, angular momentum L, spin momentum S and total momentum J for nuclear or atomic physics.... i know that whether spin is an integer or half-integer determines the particle obeying Fermi-Dirac or Bose-Einstein statistics. I know that it's a fixed, inherently true characteristic of a particle, just like rest mass is. But i've never understood what spin REALLY means, in quantum mechanics. Can anyone explain, perhaps with an analogy?