Quantitative measure of solvent polarity, based on the solvent’s hydrogen-bond-donor ability, hydrogen-bond-acceptor ability, polarizability, and dipolarity.
Source:
PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 379 (https://doi.org/10.1515/pac-2018-1010)