Definitions for "Hund's rule"
when electrons occupy atomic orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with their spins parallel. (see Aufbau principle, Hund's rule)
rule of maximum multiplicity. A rule of thumb stating that subshells fill so that the number of unpaired spins is maximized, or "spread them out and line them up."
For a set of degenerate orbitals, the lowest-energy electronic configuration will be the one in which the electrons are distributed as equally as possible amongst the degenerate orbitals.