Hindi–Urdu (Devanagari: हिन्दी-उर्दू, Nastaliq: ہندی-اردو) (also known as Hindustani) is the lingua franca of modern-day Northern India and Pakistan (together classically known as Hindustan). Modern Standard Hindi is officially registered in India as a standard written using the Devanagari script, and Standard Urdu is officially registered in Pakistan as a standard written using an extended Perso-Arabic script.
Hindi–Urdu transliteration (or Hindustani transliteration) is the process of converting text written in Devanagari script (used for Hindi) into Perso-Arabic script (used for Urdu), or vice versa. It focuses on representing the shared phonemes between those writing systems or using other writing systems, primarily Latin alphabet, in their stead. Transliteration is theoretically possible because of the common Hindustani phonology underlying Hindi-Urdu. In the present day, the Hindustani language is seen as a unifying language, as initially proposed by Mahatma Gandhi to resolve the Hindi–Urdu controversy.