Hindi (हिन्दी) is an Indo-Aryan language spoken in northern and central India, called the "Hindi belt". It's also the most widely spoken of Indian languages. Along with English it's the official language of the Indian government and one of the 22 scheduled languages specified in the Indian constitution. It is also an official language in Fiji, where it is spoken by most people of Indian descent.
Hindi evolved from Prakrit, a language derived from classic Sanskrit and old Indic dialects. It originated as local dialects such as Braj, Awadhi, and finally Khari Boli towards the end of the 10th century AD. Khari Boli, as a result of nearly a thousand years of Muslim rule, adopted Persian and Arabic words.
The word "Hindi" is often used to mean minor languages of the 'Hindi belt'. Punjabi, Bihari, and Chhattisgarhi, while sometimes recognised as distinct languages, are often considered dialects of Hindi.
Though Hindi and Urdu are considered different languages and both use different scripts, they both evolved from Khari boli and have similar grammar and basic vocabulary. Hindi has a Sanskritized vocabulary, while Urdu is Persianized. Urdu is also one of India's scheduled languages and the official language in five Indian states.
Hindi is written in the Devanagari script, which was originally used to write Sanskrit. To represent sounds that are not in Sanskrit, existing characters are used to represent those sounds. Hindi follows Western punctuation marks such as comma, colon, exclamation mark, etc. The full stop is used to end a sentence, but sometimes the traditional vertical line is also used.
Hindi sentence has a subject-object-verb structure, unlike English which generally has a subject-verb-object syntax. In some cases, verbs agree with the object of a sentence rather than the subject. Hindi has no definite article. The numeral 'one' is used as the indefinite singular article where applicable.
Hindi uses postpositions which are prepositions suffixed to nouns. Other differences include gender, honorifics, interrogatives, use of cases, and tenses.
In Hindi, there are two genders for nouns. Male human beings, male animals, and male plants are masculine. Female human beings, female animals, and female plants are feminine. Inanimate objects and abstract nouns are masculine or feminine as per convention.
Hindi has first, second, and third person pronouns for only one gender. Therefore, the same pronoun is used to refer 'him', 'her', 'it', and 'that'. The conjugated verb indicates the gender. For the second person, Hindi has three levels of honorifics: Formal and respectable form for you (आप). Just as in English, this you is used to refer both the singular and the plural. Another is the informal form of you. Similar to the formal form, it has no difference between the singular and the plural. The extremely informal form of you is tum (तुम), like the French tu.
Generally, the standard word order in Hindi is subject-object-verb, this is changed when a when a more complex sentence structure is needed. Negation is formed by adding the word nahī̃ (नहीं, no) in the appropriate place in the sentence, or by using na (न) or mat (मत) (not, don't, etc.) in some cases. The adjectives precede the nouns they qualify. Auxiliary verbs always follow the main verb. Hindi grammar allows the word order to be changed in any manner for stylistic effects.
Information: Wikipedia