In physics, a fermion is a particle with half-integral spin, i.e., an odd multiple of one-half. Examples include the electron, the proton, and the neutron.
Fermions obey the Pauli exclusion principle, which states that no two identical fermions can occupy the same quantum state. This is in contrast to identical bosons, which may occupy the same quantum state.
Fermions are named after the Italian-born physicist Enrico Fermi (1901-1954).