base peak

in mass spectrometry
https://doi.org/10.1351/goldbook.B00608
The peak in a mass spectrum corresponding to the separated ion beam which has the greatest intensity. This term may be applied to the spectra of pure substances or mixtures.
Sources:
Orange Book, 2nd ed., p. 206 (http://media.iupac.org/publications/analytical_compendium/)
PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1554 (https://doi.org/10.1351/pac199163101541)