Hindi (Hindi: हिन्दी hindī), also called Modern Standard Hindi (Hindi: मानक हिन्दी mānak hindī), is a standardised and Sanskritised register of the Hindustani language. (For information on the phonology, grammar, and other features of the spoken language, please see Hindustani language.) Hindi is one of the official languages of the Union of India, and the lingua franca of the Hindi belt languages.
Hindi is the fourth-most first language in the world, after Standard Mandarin Chinese, Spanish and English.
Hindi is considered to be a direct descendant of Sanskrit, through Sauraseni Prakrit and Śauraseni Apabhraṃśa. It has been influenced by Dravidian languages, Turkic languages, Persian, Arabic, Portuguese and English. Hindi emerged as Apabhramsha (Sanskrit:अपभ्रंश; Corruption or corrupted speech), a degenerated form of Prakrit, in the 7th century A.D. By the 10th century A.D., it became stable. Braj, Awadhi, Khari Boli etc. are the dialects of Hindi. The dialect of Hindustani on which Standard Hindi is based is Khariboli, the vernacular of Delhi and the surrounding western Uttar Pradesh and southern Uttarakhand. Urdu, literally meaning, “the language of the camp”, a dialect of Hindustani, acquired official linguistic prestige in the later Mughal period (1800s). In the late 19th century, the movement standardising a written language from Khariboli, for the Indian masses in North India, started to standardise Hindi as a separate language from Urdu, which was learnt by the Mughal elite. In 1881, Bihar accepted Hindi as its sole official language, replacing Urdu, and thus became the first state of India to adopt Hindi.
Linguistically, Hindi and Urdu are two registers of the same language. Hindi is written in the Devanagari script and uses more Sanskrit words, whereas Urdu is written in the Perso-Arabic script and uses more Arabic and Persian words. Hindi along with English is the most commonly used official language in India. Urdu is the official language of Pakistan (along with English), and is one of the 22 official languages of India.
Source: Wiki