What rule, principle or law is used to explain that an electrons will not share the same orbital if there is an empty orbital of the same energy available?

Question

Quizplus · Accepted Answer

Hund's rule explains that electrons will fill empty orbitals of the same energy before pairing up in the same orbital. This minimizes electron-electron repulsions within an atom and leads to more stable configurations.

What Rule, Principle or Law Is Used to Explain That