Hindustan pronunciation (ہندوستان or हिंदुस्तान) is a common geographic term for the northern/northwestern Indian subcontinent. The terms Hind and Hindustān were current in Persian and Arabic at the time of the 11th century Turkic conquests.
The term Hindustan traces its origin to the Hindu Kush mountains, which were designated as the lands beyond the Hindu Kush ranges. These ranges, being cumbersome and a major hurdle for the invading armies to cross over during the Moghul conquests of 10 century AD, named the land beyond the Hindu Kush as Hindustan.
Another origin traces to Hindustan being derived from the Persian word Hindū cognate with the Sanskrit Sindhu, the sacred river of the Harappa and Mohenjo-Daro civilizations. The Proto-Iranian sound change *s > h occurred between 850–600 BCE, according to Asko Parpola. Hence, the Rigvedic sapta sindhava (the land of seven rivers) became hapta hindu in Zend Avesta. It was said be the fifteenth domain created by Ahura Mazda, apparently a land of `abnormal heat'. In 515 BCE, Darius I annexed the Indus valley to his empire, calling the land Hindu from the Sanskrit name Sindhu of the Indus river. During the time of Xerxes the term was applied to the lands to the east of Indus.
In middle Persian, probably from the first century CE, the suffix -stān was added, indicative of a country or region, forming the present word Hindūstān.
In the 11th century, a satellite state of the Ghaznavids in the Punjab became known as "Hindustan", with the capital at Lahore.
The rulers of the Delhi Sultanate and the Mughal Empire called their dominion, centered around Delhi, "Hindustan".
The term "Hindustan" currently has different meanings. However, historically it has been applied to the Gangetic Plain of North India, between the Himalayas and the Vindhyas and the Indus River basin in Pakistan.
Alternatively, it may pertain to numerous aspects belonging to two geographical areas: the Indus River basin (eastern Pakistan) during medieval times, or a region in northern India, east and south of the Yamuna river, between the Vindhya mountains and the Himalayas, amongst the places where Hindustani is spoken. This abbreviated version appears in the common nationalist salutation of India, Jai Hind, coined by Major Abid Hasan Safrani of the Indian National Army as a shortened version of Jai Hindustan Ki (translation: Victory to India). It was popularized by Subhas Chandra Bose, who used it on Azad Hind Radio during the Indian independence movement. It appears in the revered song, Aye Mere Watan Ke Logon. Today, it is widely used as a salutation and a battle cry in the Indian Armed Forces. It is also commonly used to sign off at the end of major speeches.
Most formally, in the proper disciplines of Geography and History, Hindustan refers to the region of the upper and middle Ganges valley and the eastern banks of the river Indus. Hindustan by this definition is the region located between the distinct lands of Punjab in the northwest and Bengal in the north-east. So used, the term is not a synonym for the terms "South Asia", "India", or "Country of the Hindus" [sic], or of the modern-day Republic of India, variously interpreted.
In one usage among Hindustani speakers in India, the term 'Hindustani' refers to an Indian, irrespective of religious affiliation. Among non-Hindustani speakers e.g. Bengali-speakers, "Hindustani" is sometimes used to describe persons who are from the upper Ganges, also regardless of religious affiliation, but rather as a geographic term.
Hindustani is sometimes used as an ethnic term applied to South Asia (e.g., a Mauritian or Surinamese man with roots in South Asia might describe his ethnicity by saying he is Hindustani). For example, Hindoestanen is a Dutch word used to describe people of South Asian origin, in the Netherlands and Suriname.
Within Pakistan, the term "Hindustan" is sometimes used as a synonym for the modern-day Republic of India. Most Indians do call India as 'Hindustan', though Bharat is also sometimes used.
Hindustani is also used to refer to the Hindustani language (not to be confused with Hindi, which is a register of Hindustani alongside Urdu, another register of the same language), which derives from the Khariboli dialect under the Delhi Sultanate of present-day Western Uttar Pradesh, Southern Uttarakhand and Delhi areas.