soil 1. the ease with which gases, liquids, or plant roots penetrate or pass through a bulk mass of soil or a layer of soil —note since soil horizons vary in permeability, permeability should be indicated for each horizon rather than for the soil as a whole 2. the property of a porous medium itself that expresses the ease with which gases, liquids, or other substances can flow through it, and is the same as intrinsic permeability denoted by k —note permeability is measured by the rate at which a fluid of standard viscosity can move through material in a given interval of time under a given hydraulic gradient This definition last updated 07/23/2008