What is the definition of an unconfined aquifer?

An unconfined aquifer is defined as a groundwater reservoir that is not capped by a confining layer, allowing water to freely flow to the surface. It is located beneath the water table, which is the top level of saturation where groundwater fills the pores in soil and rock. An unconfined aquifer is subject to atmospheric pressure because there is no impermeable layer above it to trap pressure. As a result, water within an unconfined aquifer can fluctuate with changes in the water table due to seasonality, precipitation, and extraction. This relationship with atmospheric pressure and the lack of a confining layer are key characteristics that define unconfined aquifers and differentiate them from other types of aquifers.