Qawwali is the premier Islamic devotional music form, and -- put simply -- a form of worship. Light classical in style, usually performed in verse followed by chorus fashion, call and response, it is the foremost Islamic devotional music of the Indian sub-continent, and one of the most popular of all Muslim idioms.
Only the light classical ghazal form of Persian descent is a contender for the hearts of Muslims. Closely associated with the mystical Sufi brotherhood, the word `qawwali' derives from the Persian qaul (literally, to tell). Qawwali itself means utterance. Its singers are called qawwals. Its popularity transcends religious and geographical boundaries and Hindus, Sikhs and Muslims alike sing its praises.
... A related poetic form called tarannum -- chanted Urdu poetry -- is widely appreciated where Urdu is spoken. Being chanted (as opposed to sung) it escapes the theological debate that has dogged qawwali.
Islamic theologians have long debated whether music is prohibited or permissible. Nevertheless the faithful have long been great lovers of music. Qawwali is not the recipient of universal acceptance among Muslims or even Sufis. Of the four silsilahs (literally, chains or lines) or Sufi orders, found in any numbers in the subcontinent -- Chishti, Suhrawardi, Naqshbandi and Qadiri ... -- only the Chishtis traditionally sought ecstatic inspiration and oneness with God through music. The Suhrawardis were indifferent to music's charms. The Naqshbandis rejected it outright.