In quantum mechanics, Fermi-Dirac statistics describes the statistical behavior of a system of indistinguishable particles with a number of different states, each of which may be occupied at any one time by a single particle only (see Pauli exclusion principle). Particles that show this behavior are called fermions. Fermi-Dirac statistics is named after Enrico Fermi and Paul Dirac. Compare with Bose-Einstein statistics.