Infiltration refers to the downward entry or movement of water into the soil surface. It is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is determine by a soil characteristics including ease of entry, storage capacity, and transmission rate through the soil.
It is measure of ability of a porous material to allow fluid to pass through it. High permeability will allow fluids to move rapidly through rocks. Permeability is affected by the pressure in a rock.