Definitions for "Aquitard"
A layer of rock having low permeability that stores groundwater but delays its flow.
The less-permeable beds in a stratigraphic sequence that tend to restrict or impede groundwater flow relative to the more permeable beds that serve as aquifers.
A geological formation that (1) is much less pervious than and (2) is much thinner than the aquifer that underlies or overlies it. It acts as a semi-pervious membrane through which leakage between aquifers separated by it may occur.