Aquifer

Definition of Aquifer:

Underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt).

This is the common definition for Aquifer, other definitions can be discussed in the article

A confined aquifer is an aquifer that is overlain by a confining poorly permeable layer.

An unconfined aquifer is an aquifer extending from the land surface to the base of the aquifer.