1. The energy which is necessary to remove an electron with the Fermi energy in a solid to the energy level of an electron at rest in a vacuum outside the solid.
2. The energy required to raise an electron with the Fermi energy (average energy of electrons in a metal) in a solid to the energy level of an inactive electron in a vacuum outside the solid.

The term Fermi energy is named after Enrico Fermi (1901-1954), an Italian nuclear physicist and refers to the level in the distribution of electron energies in a solid at which a quantum state is equally likely to be occupied or empty.