The Balkan peninsula, also known as the Balkans (from the abbreviated form of the Balkan Mountains, a mountain system between Bulgaria and Serbia; from the Turkish balkan ‘mountain’ ), is a peninsula in Eastern Europe; it is bounded to the west by the Adriatic Sea, to the southwest by the Ionian Sea, to the east by the Black Sea, to the southeast by the Sea of Marmara, and to the south by the Aegean Sea.
As often happens for the peninsulas, the definition of its border on the mainland is uncertain, aggravated by the fact that it is one of its most extensive borders. Furthermore, the definition of this dividing line does not help the fact that the territory presents within it great differences and fragmentations by history, nationality, language, culture and religion of the populations who live there.
The border is usually established on the Danube and its tributary Sava. In this way, parts of Slovenia and Romania (an Eastern Romance-speaking country) are also included in this area, which however historically had to do with the Balkans only after the dissolution of the Habsburg Empire. According to geographer Vittorio Vialli, the northern boundary is represented by the geographical line Istria-Odessa. Slovenia excludes from the region the interpretation of the border that includes the Kupa River, starting it from the city of Rijeka and reaching the mouth of the Danube.  In this way it borders to the west with the so-called Italian geographical region,   which also includes territories that are not part of the Italian Republic. The political definition of the Balkans came into use in the 19th century to designate the European countries affected by the expansion and subsequent dissolution of the Ottoman Empire. 
After all, the characteristics of the territory, crossed by parallel mountain ranges that hindered the movement in a north-south direction and a uniform colonization already at the time of the Greco-Roman expansion, and its very geographical location help to explain the tormented historical events that have characterized the peninsula. 
Until 1975 the peninsula was crossed by the Balkan Express, a train departing from Vienna and arriving in Istanbul. The climate is continental in the north and east of the territory (with hot summers and very cold winters), while the western area and Greece have a Mediterranean climate.