3. Derogatory term, literally meaning black head, as in someone with black hair. Mainly used by ethnic Russians in Russia for people from the Caucasus, like Armenians, Georgians or Azerbaijanis, but also for Central Asians like Tajiks or Afghans.

Random American guy: “Wait, that guy over there doesn’t look Russian, his hair aren’t even blond, why does he speak Russian?”
Russian guy: “He is a Churka”

https://www.urbandictionary.com/define.php?term=Churka