I think the answer this question is looking for is 'aquifer', but the definition given is not completely correct. Rather than a body of water stored underground, groundwater is often stored in a layer of permeable rock, rock fractures or unconsolidated materials, such as gravel, sand, or silt. So the reference to a 'body' of water is misleading, as it give the impression that groundwater occurs as underground lakes or rivers. Although this can sometimes be the case, groundwater often exists in between small spaces in the underlying geology.
