Hindi? Urdu? Hindustani? Hindi-Urdu?
Most of the films reviewed at this site are made by the cinema industry based in Mumbai (Bombay). Their language is identified in the notes as "Hindi"—which is one label for the lingua-franca of much of north and central South Asia. This spoken language (sometimes also called "Hindustani") is commonly written in two scripts: Devanagari (a chunky, angular script identified with its Sanskrit heritage)
and Nastaliq (a flowing cursive based on the Arabic alphabet, indicative of a thousand years of Islamic cultural influence in the region).
When Hindi is written in Nastaliq, most people nowadays call it "Urdu" and DVD boxes sometimes identify film language thus (e.g., MUGHAL-E-AZAM, which is set in a 16th century Mughal court and has a highly Persianized vocabulary is said to be in "Urdu"). It is important to recognize that, political and religious differences of recent times notwithstanding, Hindi and Urdu are grammatically and practically a single language, and it seems foolish to categorize Mumbai-made "Hindi" films as being in "Urdu" whenever they happen to be about Muslims. In fact, the language of Mumbai films in general (like much of the everyday speech of north and central India) contains a large number of Persian and Arabic words (especially for romantic love — a major preoccupation of this cinema) and is thus fairly "Urdu-ized" in flavor. Rather than contribute to the further division of this unitary (and unifying) language along religious lines, we elect to simply call it "Hindi," and regret if this does not please all readers.
An illuminating article on the language and cultural heritage of Mumbai films is Mukul Kesavan's "Urdu, Awadh and the Tawaif: the Islamicate Roots of Hindi Cinema," in Forging Identities: Gender, Communities and the State, edited by Zoya Hasan. New Delhi: Kali for Women, 1994; pp. 244-257.
Also recommended (on Hindi/Urdu):
Christopher King, One Language, Two Scripts: The Hindi Movement in Nineteenth Century North India. Bombay: Oxford University Press, 1994.
Alok Rai, Hindi Nationalism. Hyderabad: Orient Longman, 2001.