An aquiclude is a geological formation that, although porous, is impermeable to water, effectively acting as a barrier to groundwater flow. Aquicludes are composed of materials like clay or shale that prevent the movement of water between aquifers. Understanding aquicludes is important in hydrogeology for managing groundwater resources and predicting the movement of contaminants.
Source Todd, D. K., & Mays, L. W. (2005). Groundwater Hydrology. John Wiley & Sons.