What term describes subsurface water that saturates geological formations?

The term that describes subsurface water saturating geological formations is groundwater. Groundwater is found in the spaces between soil particles and in the fractures of rock formations. It is a crucial component of the hydrological cycle, as it can contribute to streams, rivers, and lakes when it discharges into surface water bodies or is extracted for human use through wells.

Groundwater is distinguished from surface water, which is found on the Earth's surface in bodies such as lakes, rivers, and reservoirs. The term aquifer refers to a specific geological formation that can store and transmit groundwater, but it does not encompass all subsurface water. Soil moisture pertains to the water that is held in the upper layer of soil and is available for plants, which is different from groundwater that exists deeper underground. Thus, groundwater is the most accurate term for the subsurface water saturating geological formations.