Shortened prayer of worshippers of Cthulhu Cult. In full "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" - "In his house at R'lyeh, dead Cthulhu waits dreaming."
Cthulhu is fictional evil deity from stories of H.P. Lovecraft, first appearing in Call of Cthulhu from 1928.