hydraulic unit
as defined in Directive 2009/31/EC of the European Parliament and of the Council of 23 April…, Article 3, point (7) (Definitions)
7.
‘hydraulic unit’ means a hydraulically connected pore space where pressure communication can be measured by technical means and which is bordered by flow barriers, such as faults, salt domes, lithological boundaries, or by the wedging out or outcropping of the formation;