A strait or narrow sea between two seas, or a lake and a seas; as, the Bosporus (formerly the Thracian Bosporus) or Strait of Constantinople, between the Black Sea and Sea of Marmora; the Cimmerian Bosporus, between the Black Sea and Sea of Azof.

a strait connecting the Mediterranean and the Black Sea; separates the European and Asian parts of Turkey; an important shipping route

The Bosporus or Bosphorus, also known as the Istanbul Strait, (Turkish: Ä°stanbul BoÄŸazı or, for Ä°stanbul's inhabitants, simply BoÄŸaz; while the term BoÄŸaziçi denotes those parts of the city with view of the strait) (Greek: Βόσπορος) is a strait that forms the boundary between the European part (Rumelia) of Turkey and its Asian part (Anatolia). The world's narrowest strait used for international navigation, it connects the Black Sea with the Sea of Marmara (which is connected by the Dardanelles to the Aegean Sea, and thereby to the Mediterranean Sea). It is approximately 30 km long, with a maximum width of 3,700 metres at the northern entrance, and a minimum width of 700 metres between Kandilli and AÅŸiyan; and 750 metres between Anadoluhisarı and Rumelihisarı.