What describes a closed depression formed in an area of karst topography?

A closed depression in an area of karst topography is specifically referred to as a "sink." Karst topography forms primarily in limestone regions where dissolution of rock by water creates various landforms, including sinkholes, which are depressions or holes in the ground caused by the collapse of a surface layer. These sinks can vary in size and can be formed through processes like the erosion of soluble rocks, leading to the development of depressions that can collect water or sediment.

While the other terms have specific meanings, they do not accurately describe the distinct feature of a closed depression in karst landscapes. For example, a well is a man-made structure for accessing groundwater, a basin typically refers to a large, bowl-shaped depression often associated with sediment accumulation or water collection, and a crevice is a narrow opening or fissure in the surface, not a closed depression. Thus, the term "sink" is precisely the correct terminology to use for the closed depression in karst regions.