"Mass Flow Rate" is a measure of Mass flux. The common symbol is $\dot{m}$ (pronounced $m-dot$), although sometimes $\mu$ is used. The SI units are $kg s-1$.
$q_m = \frac{dm}{dt}$, where $m$ is mass and $t$ is time.
Applicable units are those of quantitykind:MassFlowRate
Mass Flow Rate