The word "egregore" (also "grigori") is a transliteration of the Greek word, ἐγρήγοροι (egrḗgoroi), meaning "watchers". This word appears in the septuagint translation of the Book of Lamentations, as well as the Book of Jubilees and the Book of Enoch.
Eliphas Lévi, in Le Grand Arcane ("The Great Mystery", 1868) identifies "egregors" (sic) with the tradition concerning the fathers of the nephilim, describing them as "terrible beings" that "crush us without pity because they are unaware of our existence."
The concept of the egregore was developed in works of the Hermetic Order of the Golden Dawn and the Rosicrucians, and has been referenced by writers such as Valentin Tomberg.
Gaetan Delaforge, in Gnosis (magazine) in 1987, defines an egregore as a kind of group mind which is created when people consciously come together for a common purpose."
The concept has enjoyed renewed popularity among practitioners of Chaos Magic, following the Corporate Metabolism series of articles by Paco Xander Nathan, which were published in 2001.
The result of a synergy of thought could be the most concise description of this state of mind.
Companies, political parties, religions, prayer groups, states, and clubs all can be said to have egregores. When a project "takes on a life of its own," an egregore might be said to be present. Symbolic characters such as Santa Claus and Uncle Sam could be described as egregores. Stephen King's concept of Ka-tet in The Dark Tower series could be compared to an egregore.
When these situations arise, trying to understand the group by understanding its members in isolation fails. The group can be understood by modeling the members' interactions, but the human tendency to anthropomorphize may make it more intuitive to see the group itself as having preferences for a certain outcome, regardless of its members' wishes.