Esotericism (or Esoterism) is a general term that refers to the holding of esoteric opinions or esoteric knowledge, i.e. knowledge which is available only to a narrow circle of “enlightened”, “initiated”, or specially educated people.
While many esoteric subjects have a history reaching back thousands of years, these have generally not survived as continuous traditions. Rather, they have benefited from various antiquarian revival movements, such as the resurgence of Neo-Platonism and Hermeticism, during the Italian Renaissance. In the 17th century, European esotericism was reformulated as Rosicrucianism, and later entered various strands of Freemasonry. In the 19th Century, a notable French revival in turn gave way to the Theosophy of Madame Blavatsky (which was itself again reformulated in the 20th Century), along with Anthroposophy (a synthesis of Western esoteric traditions and Theosophy, founded by Rudolf Steiner in the early part of the 20th Century) and Archeosophy (an original form of esoteric Christianity developed by Tommaso Palamidessi in the late 1960s).