The Pannonian Basin, or Carpathian Basin, is a large sedimentary basin situated in southeast Central Europe. After the WW1 and Treaty of Trianon, the geomorphological term Pannonian Plain became more widely used for roughly the same region though with a somewhat different sense, with only the lowlands, the plain that remained when the Pliocene Epoch Pannonian Sea dried out.

Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence creates a regional depression that provides accommodation space for accumulation of sediments. Over millions or tens or hundreds of millions of years the deposition of sediment, primarily gravity-driven transportation of water-borne eroded material, acts to fill the depression. As the sediments are buried, they are subject to increasing pressure and begin the processes of compaction and lithification that transform them into sedimentary rock.