Hindi Belt
The Hindi Belt or Hindi Heartland is a loosely defined linguistic region in north-central India where varieties of Hindi in the broadest sense are widely spoken. It is sometimes also used to refer to those Indian states whose official language is Standard Hindi and have a Hindi-speaking majority, namely Bihar, Chhattisgarh, Delhi, Haryana, Himachal Pradesh, Jharkhand, Madhya Pradesh, Rajasthan, Uttarakhand and Uttar Pradesh.
Hindi as a dialect continuum
Hindi, in the broad sense, is that part of the Indo-Aryan dialect continuum that lies within the cultural Hindi Belt in the northern plains of India. In the words of Masica (1991), these [languages] are the so-called regional languages of the Hindi area, sometimes less accurately called Hindi "dialects". Hindi in this broad sense is an ethnic rather than a linguistic concept.
This broad definition of Hindi is one of the ones used in the Indian census, and results in a clear majority of Indians being reported to be speakers of Hindi, though Hindi-area respondents vary as to whether they call their language Hindi or use a local language name. As defined in the 1991 census, Hindi has a broad and a narrow sense. The name "Hindi" is thus ambiguous.