What is "yagma"

The Yagmas, or Yaghmas, were a medieval tribe of Turkic people that came to the forefront of history after the disintegration of the Western Turkic Kaganate. They were one component of a confederation which consisted of Yagma, the Karluks, the Chigils and other tribes which founded the Kara-Khanid Khanate. From the seventh century until the Karakhanid period, the Yagma were recorded in Arabic, Persian, and Chinese accounts as a prominent and powerful political entity in the Tarim Basin, Dzungaria, and Jeti-su.