"Rehna Tu" is a Hindi

Hindi

Standard Hindi, or more precisely Modern Standard Hindi, also known as Manak Hindi , High Hindi, Nagari Hindi, and Literary Hindi, is a standardized and sanskritized register of the Hindustani language derived from the Khariboli dialect of Delhi...

 song composed by A. R. Rahman

A. R. Rahman

Allah Rakha Rahman is an Indian composer, singer-songwriter, record producer, musician, and philanthropist. Described as the world's most prominent and prolific film composer by Time, his works are notable for integrating eastern classical music with electronic music sounds, world music genres and...

, featuring lyrics by Prasoon Joshi

Prasoon Joshi

Prasoon Joshi is an Indian lyricist, screenwriter and advertising copywriter. A prolific Writer-Poet whose first book of 3 books "Main aur Woh" was published when he was 17 years of age, an internationally acclaimed Indian advertising professional, Bollywood film songwriter, as well as a...

 for the 2009 Bollywood

Bollywood

Bollywood is the informal term popularly used for the Hindi-language film industry based in Mumbai , Maharashtra, India. The term is often incorrectly used to refer to the whole of Indian cinema; it is only a part of the total Indian film industry, which includes other production centers producing...

 film Delhi-6

Delhi-6

Delhi-6 is a 2009 Hindi-language film directed by Rakeysh Omprakash Mehra and starring Abhishek Bachchan, Sonam Kapoor, Om Puri, Waheeda Rahman, Rishi Kapoor, Atul Kulkarni, Deepak Dobriyal and Divya Dutta. The film is reportedly based on Mehra's growing up years in Chandni Chowk area of Old...

. The song was performed by Benny Dayal

Benny Dayal

Benny Dayal is an Indian singer. He is a member of the band S5 launched by the channel SS Music. Originally from Kerala, he has worked as a playback singer with many noted composers to produce successful soundtracks.-Biography:Benny Dayal's parents hail from Kollam district, Kerala...

, Tanvi Shah

Tanvi Shah

Tanvi Shah is a popular playback singer for films in India. She is the first Indian woman to win the Grammy Awards for the lyrics of "jai ho". She has a versatile voice and can sing in Arabic, Latin, Spanish and sings a wide range of music with her band, Zahrra...

 and Rahman himself, who is the main vocalist.

"Rehna Tu" is a melody with a western base to it. The song features an instrumental

Instrumental

An instrumental is a musical composition or recording without lyrics or singing, although it might include some non-articulate vocal input; the music is primarily or exclusively produced by musical instruments....

 piece in the last two minutes. The musical instrument

Musical instrument

A musical instrument is a device created or adapted for the purpose of making musical sounds. In principle, any object that produces sound can serve as a musical instrument—it is through purpose that the object becomes a musical instrument. The history of musical instruments dates back to the...

 used by Rahman in this part and in the background of the song is Continuum Fingerboard. "Rehna Tu" was the first Asian song to have the instrument.