A fermion is any particle that has odd-half-integer (1/2, 3/2, ...) intrinsic angular momentum (spin), measured in units of h-bar. As a consequence of this odd-half-integer angular momentum, fermions obey a rule called the Pauli Exclusion Principle which states that no two fermions can exist in the same state (identical spin, color charge, angular momentum, etc.) at the same place and time. Many properties of ordinary matter arise because of this rule.
Electrons, protons and neutrons are all fermions. More generally all the fundamental matter particles, quarks and leptons, and the composite particles, baryons, are fermions.
A boson is a particle that has integer spin measured in the units of h-bar (spin=0, 1, 2...). The particles associated with the force fields, carrier particles, related to all the fundamental interactions are bosons. Composite particles with even numbers of fermion constituents, mesons, are also bosons.
A nucleus is a fermion or boson depending on whether the sum of the number of protons and neutrons is odd or even.
Bose and Fermi
Spin
