Herzegovina (Bosnian/Croatian: Hercegovina, Serbian: Херцеговина) is in Bosnia and Herzegovina. Herzegovina is divided into two parts: the Western Herzegovina, which belongs to the Federation of Bosnia and Herzegovina and the Eastern Herzegovina, belongs to the Republic of Srpska.
Herzegovina is one of the two traditional regions making up the country of Bosnia and Herzegovina (the other being, perhaps non-surprisingly, Bosnia), and forms the southern quarter of the country. It borders Croatia to west, Montenegro to southeast, and has a tiny coastline on the Adriatic, the sole window of the country to the sea.
Although mass displacements and ethnic cleasings of the locals took place during the Yugoslav Wars of 1992–1995, the region still has a multi-ethnic community (though not to the extend that it was before the war) and is roughly divided in half between the two political entities of the country: Bosniak/Croat-majority Federation occupies the western half, while Serb-majority Republic of Srpska occupies the eastern half.
Although slightly inland as it is separated from the coastline by a portion of Croatia, southern parts of Herzegovina enjoy a mild Mediterranean climate while northern parts are under influence of continental climate with cold winters.
All three major languages of the country (Bosnian, Croatian, Serbian) are spoken natively in the region. As these three languages are mutually intelligible, travellers speaking any of them will have no problems in communicating with locals throughout the region. However, as local Serbs prefer Cyrillic alphabet over Roman one, you may need to memorise at least a few key phrases in Cyrillic for a smooth experience in eastern parts of Herzegovina.