Turan (in ) is the ancient Iranian name for the Eastern nomads. In modern discourse, it is primarily an ideological term designating Turkic, Mongolic and Finno-Ugric languages and people more or less indiscriminately, implying a common ancestry and common culture of the various ethnicities in question.
In the hymns of the Avesta, the adjective Tūrya is attached to various enemies of Zoroastrism like Fraŋrasyan (Shahnameh: Afrāsīāb). The word occurs only once in the Gathas, but 20 times in the later parts of the Avesta. Apparently there is no ethnic difference between the Tūrya and the Ārya in the Avesta, both having Iranian names and being related genealogically.
Linguists normally derive the word from the Indo-Iranian root *tūra- "strong, quick". The similarity between the words Tūrya and Türk is considered accidental by most scholars, and it is doubtful whether Tūrya was applied regularly to Turkic people before the late Sassanid period. However, this is contested by the adherents of the Pan-Turkists and their controversial Turanian theory (see below).
In the Middle Persian epic Shahnameh, the term Tūrān ("land of the Tūrya" like Ērān, Īrān = "land of the Ārya") refers to the inhabitants of eastern-Iranian border, referring to the Kushan Empire, pointing to a time when those areas where inhabited by mostly Iranian nomadic tribes such as Scythians.
According to the foundation myth given in the Shahnameh, King Firēdūn (= Avestan Θraētaona) had three sons, Salm, Tūr and Ēraj, among whom he divided the world: Asia Minor was given to Salm, Kushan (including India) to Tūr and Iran to Ēraj. The older brothers killed the younger brother, but he was revenged by his grand-son, and the Iranians became the rulers of the world. However, the war continued for generations.
Since early 20th century, the word Turan was borrowed by the western languages as a general word for Central Asia. Accordingly, the phrase Turan Plain or Turan Depression is a geographical term referring to a part of Central Asia.
The term Turanian was formerly used by European (especially German, Hungarian and Slovak) ethnologists, linguists and Romantics to designate populations speaking Uralic or Altaic languages (and the languages themselves).
Even though the linguistic usage of the word Turanian is hardly accepted in the scholarly community anymore, it is still rather vivid outside of the academia, especially in the internet. Thus, there is a wide-spread popular theory, which one may call the Turanian theory, that ascribes a common origin to the Turkic, Mongolic, Ugric and Sumerian languages and people, normally including the extinct Scythian, Sarmatian and Median languages as well (which are traditionally classed with the Iranian language group). The proponents of the Turanian theory are rather sceptical of the methodology of traditional comparative linguistics, which they describe as "Indo-European-centric".
Combined with physical anthropology, the concept of the Turanian mentality has a clear racist potential. Thus, the scholar J.W. Clackson described the Turanid or Turanian race in the following words ("The Iran and Turan", Anthropological Review 6:22 (1868), p. 286):
In recent times, the word Turanian is sometimes used to express a pan-Altaic nationalism (theoretically including Manchurians and Mongols in addition to Turks - and potentially Japanese and Koreans), though no political organization seems to have adopted such an ambitious platform.
Turan (Landschaft) | توران | Touran | Turán | Turan