Arran (Middle Persian form; Persian: اران or اردان), also known as Aran or Ardan, was a geographical name used in ancient and medieval times to signify a historically-Iranian[1] region which lay within the triangle of land, lowland in the east and mountainous in the west, formed by the junction of the Kura and Aras rivers,[2] including the highland and lowland Karabakh,[2] Mil plain and parts of the Mughan plain. In pre-Islamic times, it corresponded roughly to the territory of the modern-day Republic of Azerbaijan.[2] The term is the Middle Persian[3][4] equivalent to the Greco-Roman Albania. It was known as Aghvania, Alvan-k[5] in Armenian, and Al-ran[5][2] (Arabized form of Arran[3]) in Arabic.
Today, the term Aran is mainly used in Azerbaijan to indicate territories consisting of Mil and Mughan plains (mostly, Beylagan, Imishli, Kurdamir, Saatly, Sabirabad provinces of the Republic of Azerbaijan). It has also been used by Iranian historian Enayatollah Reza to refer to the country of Azerbaijan, freeing the name "Azerbaijan" to refer to a region within Iran.[6] The bulk of the territory of the republic of Azerbaijan was the historic Shirvan, as well as Quba/Qubbah).
The name Azerbaijan was also adopted for Arrān, historically an Iranian region, by anti-Russian separatist forces of the area when, on 26 May 1918, they declared its independence and called it the Democratic Republic of Azerbaijan.