A property which qualitatively indicates the degree to which a substance is extracted. The term is imprecise and generally used in a qualitative sense. It is not a synonym for fraction extracted.
Source:
PAC, 1993, 65, 2373. 'Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)' on page 2382 (https://doi.org/10.1351/pac199365112373)