What does aquifer mean?
<answer> A ​layer of ​rock, ​sand, or ​earth that ​contains ​water or ​allows ​water to ​pass through it. <context> aquifer noun [C]. › a ​layer of ​rock, ​sand, or ​earth that ​contains ​water or ​allows ​water to ​pass through it. (Definition of aquifer from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press).