A fermion is any particle of matter that is characterized by spin in odd half-integer quantum units (1/2,3/2,5/2, etc). Fermions were named
by Paul Dirac in 1947 after the Italian physicist
Enrico Fermi. They obey the Pauli
exclusion principle and Fermi-Dirac
statistics, and have antisymmetric wavefunctions.
Quarks, leptons (such as the electron), and baryons (such as the proton and neutron) are all fermions. Compare with boson.