Transmissivity; storativity; specific yield কী?

The transmissivity of an aquifer of thickness $b$ is $T = Kb$, the flow per unit width under unit gradient, in $\mathrm{m}^{2}/\mathrm{d}$. Its storativity (or storage coefficient) $S$ is the volume of water released per unit area of the aquifer when the head falls by one unit; it is dimensionless. The specific yield $S_y$ of a rock is the volume of water that drains from it by gravity per unit volume when the water table falls through it.