Final answer:
An aquifer is a unit of earth material that is both porous and permeable, allowing it to store and transmit groundwater. Sedimentary rocks like sandstone and limestone are examples of permeable materials that make good aquifers, while impermeable materials like shale or un-fractured igneous or metamorphic rock act as confining layers.
Step-by-step explanation:
A unit of earth material that is both porous and permeable and thus both stores and transmits groundwater is called an aquifer. Aquifers are underground layers of rock or sediment that can hold water in the spaces between their particles or in the fractures within them. Sedimentary rocks like sandstone and limestone are examples of permeable materials that make good aquifers, while impermeable materials like shale or un-fractured igneous or metamorphic rock act as confining layers and prevent the flow of water.