Fermi heap and Fermi hole
Fermi heap and Fermi hole refer to two closely related quantum phenomena that occur in many-electron atoms. They arise due to the Pauli exclusion principle, according to which no two electrons can be in the same quantum state in a system (which, accounting for electrons' spin, means that there can be up to two electrons in the same orbital).
Source: Wikipedia — Fermi heap and Fermi hole (CC BY-SA 4.0)