What term describes areas where water collects underground?

The term that best describes areas where water collects underground is "aquifers." Aquifers are geological formations that can hold and transmit water, serving as a vital source of groundwater. They are typically composed of porous materials such as sand, gravel, or limestone, which allow water to move through the spaces between the particles.

While "zones of saturation" refers to areas where all the spaces in soil or rock are filled with water and is related to aquifers, it is not the term that specifically designates the underground reservoirs themselves. "Groundwater basins" are broader geographic areas that may encompass multiple aquifers but do not specifically refer to the water-holding characteristics. "Wetlands," on the other hand, refer to areas where water is present at or near the surface for extended periods, but they are not underground reservoirs like aquifers.

Thus, when considering the true nature of underground water collection, aquifers provide a clearer and more precise term, making it the correct answer in this context.