An aquifer is a group, a part or the whole formation that contains enough saturated penetrable material able to contain and yield sufficient quantities of water. It is a conjunction of two Latin words, "aqua" or water and "ferre" which means to bear or carry. Aquifers are very important underground reservoir resources of water that can be exploited. Some common mineral substances found where aquifers are present are; sand, sandstone, carbonate, igneous and metamorphic rock. 
Anatomy of an Aquifer
It is through water-bearing rocks that allow the transit of water to the surface of our Earth. Many geological structures exist that we use to further determine the location of various components that make up an aquifer.  
Since aquifers generally run horizontally underneath the ground, a confined aquifer is one with impermeable rock above and below it. The water source is usually in mountainous areas where the aquifer strata is tilted upward and can collect ground water. As the water flows down into the confined aquifer, pressure builds. The water will rise by itself through cracks in the over head rock and emerge as Artesian springs or flow from drilled wells.
An unconfined aquifer is one that does not have internal pressure. This is where wells and other pumping mechanisms are used to bring the water to the land surface or what is the top of the water table.
The water table is upper surface of water in an unconfined aquifer open to the surface of the earth.
The area of water underneath the water table, not including observable water sources on the surface but rather it is in reference to what lies underground connected to it.
Ground water occurs many places on Earth being responsible for springs or creeks, rivers, lakes and ultimately oceans.  Two main characteristics of rocks relate to the presence and movement of ground water. One is porosity, or the size and amount of void spaces in-between rocks, and the second has to do with permeability which is the ease at which water can move through the rock or rocks porosity.
The springs of the great deep mentioned in Genesis 7:11 of the Bible are no different than what we consider aquifers. However the size and quantity may have been different due to the amount of water needed for the flood which ultimately covered the entirety of Earth during the time of Noah. These massive underground aquifers being mentioned in different terms during ancient periods of our history is a way to determine that people living at the time were aware of these precious resources.
- Aquifer Basics by U.S. Department of the Interior, U.S. Geological Survey
- Waller, Roger M., Ground Water and the Rural Homeowner, Pamphlet, U.S. Geological Survey, 1982
- Ground-water aquifers by U.S. Department of the Interior, U.S. Geological Survey
- Aquifer Basics: Ground Water by U.S. Department of the Interior, U.S. Geological Survey
- Aquifer; Source of Pure Water by Gulf of Maine Research Institute; 1998