Article on the Yazidi religious beliefs
Hunted by militants from the Islamic State, thousands of people from the Yazidi community have fled to the slopes of Iraq's Mount Sinjar, where they are caught between the prospect of death by dehydration and murder at the hands of the group formerly called ISIS. In the months since its rise, the Sunni-identified Islamic State has gone after many religious and ethnic minorities in Iraq and Syria, including Christians, Shiite Muslims, Shiite Turkmen, Shiite Shabaks, and of course the Yazidi.
Also called Yezidi, Daasin, or Ezidi, the Yazidi are a Kurdish-speaking ethnoreligious community based in Northern Iraq who practice a syncretic religion influenced by pre-Islamic Assyrian traditions, Sufi and Shiite Islam, Nestorian Christianity, and Zoroastrianism. Their rich oral tradition is their primary way of passing on their beliefs, which makes it complicated for scholars and historians to pin down the nuances of their religion.
http://www.huffingtonpost.com/2014/08/13/yazidi-religious-beliefs_n_5671903.html
Don't know about you, but I knew zero about this group