Urdu /ˈʊərduː/ (اُردُو [ˈʊrd̪u] )), or more precisely Modern Standard Urdu, is a standardized register of the Hindustani language that is associated with the Muslim religion. It is the national language and lingua franca of Pakistan, and an official language of five Indian states and one of the 22 scheduled languages in the Constitution of India. Apart from specialized vocabulary, it is mutually intelligible with another register of Hindustani, Standard Hindi, which is associated with the Hindu religion. Since the end of the Mughal period in the nineteenth century, the varieties of Hindustani have been the lingua franca for much of South Asia. The two varieties of Hindustani are nearly identical in basic structure and grammar, and at a colloquial level also in vocabulary and phonology. The population of Hindi-Urdu speakers is the fourth largest of the languages of the world, after Mandarin Chinese, English and Spanish.
The word Urdu is derived from the same Turkish word ordu (army) that has given English horde.Since the establishment of the Delhi Sultanate and the Mughal Empire until the British Raj, Hindustani, written in the Urdu script, was the language of both Hindus and Muslims. The language was variously known as Hindi, Hindavi, Urdu, and Dehlavi. The communal nature of the language lasted until it replaced Persian as the official language in 1837 and was made coofficial along with English. This triggered a Hindu backlash in northwestern India, which argued that the language should be written in the native Devanagari script. Thus a new literary register, called "Hindi", replaced traditional Hindustani as the official language of Bihar in 1881, establishing a sectarian divide of "Urdu" for Muslims and "Hindi" for Hindus, a divide that was formalized with the division of India and Pakistan after independence (though there are Hindu poets who continue to write in Urdu to this day). At independence, Pakistan established a highly Persianized literary standard of Urdu as it official language.
There are between 60 and 70 million native speakers of Urdu: there were 52 million in India per the 2001 census, some 6% of the population; 13 million in Pakistan in 2008, or 8%; and several hundred thousand in the United Kingdom, Saudi Arabia, United States, and Bangladesh, where it is called "Bihari". However, a knowledge of Urdu allows one to speak with far more people than that, as Hindi-Urdu is the fourth most commonly spoken language in the world, after Mandarin, English, and Spanish.
Owing to interaction with other languages, Urdu has become localized wherever it is spoken, including in Pakistan itself. Urdu in Pakistan has undergone changes and has lately incorporated and borrowed many words from Pakistani languages like Pashto, Punjabi, Sindhi and Balti as well as former East Pakistan (now Bangladesh) Bengali language, thus allowing speakers of the language in Pakistan to distinguish themselves more easily and giving the language a decidedly Pakistani flavour. Similarly, the Urdu spoken in India can also be distinguished into many dialects like Dakhni (Deccan) of South India, and Khariboli of the Punjab region since recent times. Because of Urdu similarity to Hindi, speakers of the two languages can easily understand one another if both sides refrain from using specialized vocabulary. The syntax (grammar), morphology, and the core vocabulary are essentially identical. Thus linguists usually count them as one single language and contend that they are considered as two different languages for socio-political reasons. In Pakistan Urdu is mostly learned as a second or a third language as nearly 93% of Pakistan population has a mother tongue other than Urdu.