Esotericism or Esoterism signifies the holding of esoteric opinions or beliefs, that is, ideas preserved or understood by a small group or those specially initiated, or of rare or unusual interest.The term derives from the Greek (esôterikos), a compound of (esô): "within", thus "pertaining to the more inward", mystic. Its antonym is "exoteric".
The term can also refer to the academic study of esoteric religious movements and philosophies, or more generally of alternative or marginalized religious movements or philosophies whose proponents distinguish their beliefs, practices, and experiences from mainstream institutionalized traditions.
Examples of esoteric religious movements and philosophies include Alchemy, Astrology, Anthroposophy, early Christian mysticism, Gnosticism, Magic, Mesmerism, Rosicrucianism, Taoism, Swedenborgianism, Spiritualism, the Alawites, the Christian Theosophy of Jacob Böhme and his followers, and the Theosophical currents associated with Helena Blavatsky and her followers. There are competing views regarding the common traits uniting these currents, not all of which involve "inwardness", mystery, occultism or secrecy as a crucial trait.
Plato, in his dialogue Alcibíades (circa 390 BC), uses the expression ta esô meaning "the inner things", and in his dialogue Theaetetus (circa 360 BC) he uses ta exô meaning "the outside things". Aristotle applied this distinction to his own writings. The probable first appearance of the Greek adjective esôterikos is in Lucian of Samosata's "The Auction of Lives", § 26, written around AD 166.
The term esoteric first appeared in English in the 1701 History of Philosophy by Thomas Stanley, in his description of the mystery-school of Pythagoras; the Pythagoreans were divided into "exoteric" (under training), and "esoteric" (admitted into the "inner" circle). The corresponding noun "esotericism" was coined in French by Jacques Matter in 1828 and popularized by Eliphas Levi in the 1850s.. It entered the English language in the 1880s via the works of theosophist Alfred Sinnett.