Zeeman effect

https://doi.org/10.1351/goldbook.Z06739
The splitting or shift of spectral lines due to the presence of an external magnetic field.
Sources:
Orange Book, 2nd ed., p. 122 (https://media.iupac.org/publications/analytical_compendium/)
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2284 (https://doi.org/10.1351/pac199668122223)