Listing says Cistern on property. What is a Cistern?

A Cistern is a reservoir or tank for holding water, especially for catching and holding rain water for later use.  These are very common on larger properties with gardens or farm property. I have seen cisterns in old city homes.  They have to be closed and they are not drinking water unless they are sealed and are designed specifically for such.  A cistern is not a well as it not driven by a water table but a rather a run off or catch from incoming water elsewhere.  Cisterns can be overflows for wells.