It is the plural of Chií. It's the same as Shiites. They are the followers of Shia i.e. the Islamist movement followers of Ali and who intended Mahoram's successors to be his descendants or relatives. They are adversaries of sunnis or Sunnis.
Shia-belonging to the Shia Muslim, who recognizes Muhammad's son-in-law, "Ali", and his descendants, the "Imanes", as the true successors and legitimate heirs of Islam-