A general reaction by which a group attached to the alpha carbon of an excited chromophore is expelled either as an odd electron species or as an anionic species. This reaction should be distinguished from an α-(alpha-)cleavage.
Source:
PAC, 1988, 60, 1055. 'Glossary of terms used in photochemistry (Recommendations 1988)' on page 1059 (https://doi.org/10.1351/pac198860071055)