"A confining bed that retards but does not prevent the flow of water to or from an adjacent aquifer; a leaky confining bed. It does not readily yield water to wells or springs, but may serve as a storage unit for ground water (AGI, 1980). See preferred term confining unit" (WMO, 1974)
World Meteorological Organization, 1974, International glossary of hydrology: Geneva, Switzerland, World Meteorological Organization No. 385.