fermion

The particle-physics term fermion refers to a particle with half-integer spin, i.e., 1/2 different than some integer (1/2, 3/2, -1/2, etc.). The particle-physics term boson refers to a particle with full-integer spin (1, 2, 3, etc.). An elementary fermion is one that is an elementary particle, and a composite fermion is one that is a composite particle (formed of multiple elementary particles whose spins sum to a half-integer number), these two categories sharing the characteristics associated with half-integer spin, including adherence to Fermi-Dirac statistics. Example elementary fermions include any of the quarks and leptons. Baryons are a class of composite fermions. Electrons, protons, and neutrons are fermions. Atomic nuclei are composite fermions if their mass number is odd. (Nuclei with even mass numbers are composite bosons).