Change in volume of a system when a small amount of component is added divided by the mass of the added component. The systematic name is partial massic volume.
Source:
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)