Dune: Prophecythrows a lot of new Dunelore at us, from the Butlerian Jihad fought against thinking machines to the beginnings of the Sisterhood that will one day become the Bene Gesserit.

However, one of the biggest new terms we learn in the first episode is "Tiran-Arafel," a word uttered by Mother Superior Raquella Berto-Anirul (Cathy Tyson) on her deathbed. The warning accompanies a vision of the Sisterhood's destruction, suggesting that whatever Tiran-Arafel is, it's nothing good.