Bosnia and Herzegovina is an almost landlocked country – it has a narrow coast at the Adriatic Sea, about 20 kilometres (12 miles) long surrounding the town of Neum. It is bordered by Croatia to the north, west and south, Serbia to the east, and Montenegro to the southeast. In the central and eastern interior of the country the geography is mountainous, in the northwest it is moderately hilly, and the northeast is predominantly flatland. The inland, Bosnia, is a geographically larger region and has a moderate continental climate, with hot summers and cold and snowy winters. The southern tip, Herzegovina, has a Mediterranean climate and plain topography.
The name is believed to have derived from the hydronym of the river Bosna coursing through the Bosnian heartland. According to philologist Anton Mayer the name Bosna could derive from Illyrian *"Bass-an-as"), which would derive from the Proto-Indo-European root "bos" or "bogh"—meaning "the running water". According to English medievalist William Miller the Slavic settlers in Bosnia "adapted the Latin designation [...] Basante, to their own idiom by calling the stream Bosna and themselves Bosniaks [...]".
The name Herzegovina ("herzog's [land]", from German word for "duke") originates from Bosnian magnate Stjepan Vukčić Kosača's title, "Herceg (Herzog) of Hum and the Coast" (1448). Hum, formerly Zahumlje, was an early medieval principality that was conquered by the Bosnian Banate in the first half of the 14th century. The region was administered by the Ottomans as the Sanjak of Herzegovina (Hersek) within the Eyalet of Bosnia up until the formation of the short-lived Herzegovina Eyalet in the 1830s, which remerged in the 1850s, after which the entity became commonly known as Bosnia and Herzegovina.