Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant rocks, such as quartzite, given the right conditions. Subterranean drainage may limit surface water, with few to no rivers or lakes. However, in regions where the dissolved bedrock is covered (perhaps by debris) or confined by one or more superimposed non-soluble rock strata, distinctive karst features may occur only at subsurface levels and be totally missing above ground.
The study of karst is considered of prime importance in petroleum geology since as much as 50% of the world's hydrocarbon reserves are hosted in porous karst systems.
The English word karst was borrowed from German Karst in the late 19th century. The German word came into use before the 19th century. According to the prevalent interpretation, the term is derived from the German name for the Karst region (Italian: Carso), a limestone plateau above the city of Trieste in the northern Adriatic (now located on the border between Slovenia and Italy, in the 19th century it was part of the Austrian Littoral). Scholars disagree, however, on whether the German word (which shows no metathesis) was borrowed from Slovene.
The Slovene common noun kras was first attested in the 18th century, and the adjective form kraški in the 16th century. As a proper noun, the Slovene form Grast was first attested in 1177, referring to the Karst Plateau—a region in Slovenia partially extending into Italy, where the first research on karst topography was carried out. The Slovene words arose through metathesis from the reconstructed form *korsъ, borrowed from Dalmatian Romance carsus. Ultimately, the word is of Mediterranean origin, believed to derive from some Romanized Illyrian base. It has been suggested that the word may derive from the Proto-Indo-European root karra- "rock". The name may also be connected to the oronym Kar(u)sádios oros cited by Ptolemy, and perhaps also to Latin Carusardius.