IPSOS, meaning "themselves", is the magical formula of the Aeon of Ma'at as transmitted by Nema in her inspired magical work, Liber Pennae Praenumbra. It is used by the Horus-Maat Lodge and Kenneth Grant's Ordo Templi Orientis.
Within the system of Thelema, history is broken down into a series of Aeons, each with its own dominant concept of divinity and its own magical formula of redemption and advancement. According to Aleister Crowley, the last three Aeons have been (1) the Aeon of Isis, (2) the Aeon of Osiris, and (3) the current Aeon of Horus which began in 1904 with the writing of The Book of the Law.
According to Grant, the word IPSOS was received by initiates who were in communication with extraterrestrial intelligences. He equates the word with part of a cryptic cipher in Liber AL (II, 76), RPSTOVAL, by virtue of the fact that in the qabalistic art of gematria, both evaluate to either 696 or 456, depending on whether an 'S' in each is taken as the Hebrew letter shin or samekh.