Fermi hole

A Fermi hole is a place in space where there are no electrons. This happens because of an effect called the Pauli Exclusion Principle. This principle says that no two electrons can have exactly the same energy, so when a lot of electrons have the same energy and try to fit in the same area of space, some of them must go somewhere else. This causes a Fermi hole, which is an area of space that doesn't have any electrons in it.