Eso = Hidden
Exo = Revealed
Esoteric Knowledge = Hidden, Arcane, Occult Knowledge.
Satanism, Luciferianism & Occultism all fall into this category. People who practice esoteric religions are Luciferians such as theosophists in the Theosophical Society & Lucis Trust, Occultists such as the Church of Satan, and secret societies such as Freemasonry, Skull & Bones and the Thule Society, among many others.