Bosnia (Bosnian and Croatian: Bosna, Serbian: Босна; pronounced [bɔ̂sna]) is the northern region of Bosnia and Herzegovina, encompassing roughly 80% of the country; the other eponymous region, the southern part, is Herzegovina. Bosnia is an informal term for the whole country. The two regions have formed a geopolitical entity since medieval times, and the name "Bosnia" commonly occurs in historical and geopolitical senses as generally referring to both regions (Bosnia and Herzegovina). The official use of the combined name started only in the late period of Ottoman-rule.