Historically, a tawaif was a courtesan of the Muslim noble classes in South Asia, particularly during the Mughal era. They were known to be very knowledgeable in North Indian forms of singing, dance (usually kathak), and Urdu poetry. The tawaif culture was made famous by the Indian films Pakeezah and Umrao Jaan.
Today, the term in Urdu is almost synonymous with prostitute.
See also