an underground bed or layer yielding ground water for wells and springs etc.; as, the Oglala aquifer. The water contained in an aquifer may be of great age, and in such cases is sometimes called fossil water.

An underground stratum of rock or sediment that contains water and transmits water readily.

a subsurface permeable unit which is capable of transmitting significant quantities of groundwater.

A permeable body of rock or regolith that both stores and transports groundwater.