## Wikipedia - Scambio di materia (it) transfer

https://doi.org/10.1351/goldbook.T06439
Movement of a component within a system or across its boundary. It may be expressed using different kinds of quantities, e.g rates of change $$\frac{\text{d}Q}{\text{d}t}$$ or $$\frac{\Delta Q}{\Delta t}$$. Examples are: mass rate, $$\frac{\text{d}m_{\text{B}}}{\text{d}t}$$ or $$\frac{\Delta m_{\text{B}}}{\Delta t}$$; substance rate, $$\frac{\text{d}n_{\text{B}}}{\text{d}t}$$ or $$\frac{\Delta n_{\text{B}}}{\Delta t}$$.
Source:
PAC, 1992, 64, 1569. (Quantities and units for metabolic processes as a function of time (IUPAC Recommendations 1992)) on page 1573 [Terms] [Paper]