The ease with which a fluid can pass through a porous medium and is defined as the volume of fluid discharged from a unit area of an aquifer under unit hydraulic gradient in unit time (expressed as m3/m2/d or m/d); it is an intrinsic property of the porous medium and is dependent of the properties of the saturating fluid.
Permeability is not to be confused with hydraulic conductivity. While similar, permeability considers the properties of the fluid being transmitted (density, viscosity and temperature); hydraulic conductivity relates specifically to the movement of water. Permeability is relevant to multiphase flow systems which include gas, oil and water phases.
Why is permeability important?
Permeability provides an indication of the ease with which fluid moves through the subsurface.