Dervish

Dervish, Darvesh, or Darwīsh (from , "Darvīsh") in Islam is a type of Sufi. 
It is someone living a Sufi Muslim ascetic way or "Tariqah". They are poor, and live simply. In this respect, dervishes are most similar to mendicant friars in Christianity, or Hindu/Buddhist/Jain sadhus.
Whirling dervishes.
The whirling dance that is associated with dervishes is best known in the West by the performances of the Mevlevi order in Turkey. It is part of a ceremony known as the Sema. It is also done by other orders. The Sema is only one of many Sufi ceremonies performed to try to reach religious ecstasy ("majdhb", "fana"). 
The name "Mevlevi" comes from the Persian poet Rumi, who was a dervish himself. This practice, though not intended as entertainment, has become a tourist attraction in Turkey.