This term is not recommended and should not be used as a synonym for partition constant, partition ratio or distribution ratio.
See also: distribution constant
Sources:
PAC, 1993, 65, 2373. 'Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)' on page 2385 (https://doi.org/10.1351/pac199365112373)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 986 (https://doi.org/10.1351/pac199668040957)