Special case of nucleofugality, describing the relative rates of transfer of a proton (more generally: hydron) from a series of Brønsted acids
\(\ce{H-X}\) to a common Brønsted base.
Note:
This term has the advantage over the commonly used "kinetic acidity" that philicity and fugality are associated with kinetics, while acidity and basicity are associated with thermodynamics.
See also: protophilicity
Source:
PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 487 (https://doi.org/10.1515/pac-2018-1010)