An ion formed by interaction of two species, usually an ion and a molecule, and often within the ion source, to form an ion containing all the constituent atoms of one species as well as an additional atom or atoms.
Source:
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 1549 (https://doi.org/10.1351/pac199163101541)