Aquifer (Artesian): An aquifer that is bounded above and below by impermeable rock or sediment layers. The water in the aquifer is also under enough pressure that, when the aquifer is tapped by a well, the wate . . . View Full Definition
Aquifer (Unconfined): An aquifer that is not overlain by an impermeable rock unit. The water in this aquifer is under atmospheric pressure and is recharged by precipitation that falls on the land surface directly . . . View Full Definition
Aquifer (Confined): An aquifer that is bounded above and below by impermeable rock or sediment layers. There may or may not be enough pressure in the aquifer to make it an 'artesian aquifer'.
Aquifer: An underground water-bearing layer of rock, including gravel and sand, that will yield water in usable quantity. Aquifers are sources of water for wells and springs.