The volume of an (isolated) specified component (C) divided by the mass of the system (S), e.g. patient–blood volume content. Volume content should not be confused with specific volume (or massic volume), which is the volume of the system divided by the mass of the system.
PAC, 1979, 51, 2451. 'Quantities and Units in Clinical Chemistry' on page 2474 (https://doi.org/10.1351/pac197951122451)