A doline, sink or sinkhole is a closed depression draining underground in karst areas. It can be cylindrical, conical, bowl- or dish-shaped. The diameter ranges from a few to many hundreds of meters.
The name doline comes from dolina, the Slovenian word meaning valley. So this was originally a colloquial Slovenian word which was used by the geologists to describe a geologic feature. Locus typicus (type locale) is unknown, because the term is old, but it is definitely located in Slovenia.
There are two different mechanisms for the forming of dolines, dolines caused by solution and dolines caused by a collapse. The second is often called sinkhole, because the ground sinks.