Muadru was an ancient religion or team of humans. During the Old Empire, mystics traveled throughout the planets of the Known Universe and left obscure markings and runestones on several planets. The spiral was their sacred symbol.
During the Butlerian Jihad, Grand Patriarch Iblis Ginjo mentioned that such runestones prophesied the end of the war, and asked Cogitor Kwyna to translate and give insight about them. However Ginjo used the texts of these inscriptions out of context.
The term "Muadru" seems to be related to the Muadh Quran Faith and the ruh-spirit of Fremen-religion, hinting to a connection between the Muadru and the second or even first islamic movement.Thus Muadru can be understood as "Companion or disciple of the Spirit or Soul".