Generally, all subsurface water as distinct from Surface Water; specifically, the part that is in the saturated zone of a defined aquifer.
Water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper level of the saturate zone is called the Water Table.
Water stored underground in rock crevices and in the pores of geologic materials that make up the earth’s crust. Ground water lies under the surface in the ground’s Zone of Saturation, and is also referred to as Phreatic Water.