Definition: "Aquifer" in Greek literally means "well." It refers to a groundwater source that permeates the ground surface, allowing water to flow through it and storing enough underground water for long periods without running out. The term generally refers to aquifers that are not easily accessible by humans (like the ones found in wells or springs), yet they can be found on land. Aquifer is also used as a term for underground reservoirs of water, such as reservoirs, groundwater tanks, and dams used to store water during drought periods. For instance, the "aquifer" that holds underground water for a long period is called an aquifer storage system or an aquifer reservoir. In both contexts, this means the underground space where water resides. The term comes from Greek roots meaning well, well-drilled (meaning water was previously drained) and it describes an area of land that has been dug to provide access for drinking, irrigation, transportation, and other purposes.