mean mass rate, \(\frac{\Delta m}{\Delta t}\)

https://doi.org/10.1351/goldbook.M03784
The mass of a specified component changed in or moved to or from a system divided by the time during which the component was changed or moved.
Source:
PAC, 1979, 51, 2451. 'Quantities and Units in Clinical Chemistry' on page 2474 (https://doi.org/10.1351/pac197951122451)