This is a more polite term for the Kurdish dialect (some would even call it a language) also known by the more popular, but somewhat derogatory, term Zaza (literally "stutterer," for the frequency of the z sound in the speech). Dimili is spoken in the northwestern provinces of Turkey (in particular the former Dersim, now Tunceli) by both Alevi and Sunni Kurds and also by Alevi Turks. Dimili is related to the Kurdish dialect Gurani spoken in some of the southeastern Kurdish areas in Iran and neighboring areas in Iraq. Dimili and Gurani are probably older Kurdish dialects, but most Kurds now speak Kurmanji or Sorani. The term Dimili is possibly associated with the Dailamites, who were a people from the Alburz Mountains just south of the Caspian Sea and probably precursors of some of today's Kurds.
Some would consider the Dimili to be a separate ethnic group from the Kurds. Turkish authorities certainly encourage such a view as a divide-and-rule tactic. Dimili are more frequently known as sedentary farmers than are most other Kurds. There may be some three to four million Dimili at the present time.
Historical Dictionary of the Kurds. Michael M. Gunter.