Minimum photon energy required to liberate an electron from the surface of a conducting solid by absorption of that photon.
See also: thermionic work function
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1828 (https://doi.org/10.1515/pac-2019-0404)