What is "foiba"

n. (context geology English) A deep sinkhole

A foiba (plural: foibas or foibe) is a type of deep natural sinkhole, doline, or sink, and is a collapsed portion of bedrock above a void. Sinks may be a sheer vertical opening into a cave, or a shallow depression of many hectares. They are common in the Kras (Carso) region, a karstic plateau region shared by Italy, Slovenia, and Croatia.