The name derives from a local geological feature, a type of deep karst sinkhole called foiba. The term includes by extension killings in other subterranean formations, such as the Basovizza "foiba", which is not a true foiba but a mine shaft. The terror spread by the disappearances and the killings eventually contributed to an atmosphere sufficient to cause the majority of the Italians of Istria, Rijeka and Zadar to flee to other parts of Italy or the Free Territory of Trieste.