Esotericism signifies the holding of esoteric opinions that is, ideas preserved or understood by a small group of those specially initiated, or of rare or unusual interest.: The term derives from the Greek, either from the comparative ἐσώτερος "inner", or from its derived adjective ἐσωτερικός, "pertaining to the innermost". The term can also refer to the academic study of esoteric religious movements and philosophies, or to the study of those religious movements and philosophies whose proponents distinguish their beliefs, practices, and experiences from mainstream exoteric and more dogmatic institutionalized traditions.
Since the field of esotericism is not a single tradition but a vast array of often unrelated figures and movements, there is no single historical thread underlying them all.The developments that one might wish to emphasize in drawing up a history of esotericism furthermore depends on whether esotericism in the dictionary or the scholarly sense is intended.:Several historically attested religions emphasize secret or hidden knowledge, and are thus esoteric in the dictionary sense, without necessarily being esoteric movements in the scholarly sense of the word. Thus, the Roman Empire had several mystery religions which emphasized initiation. Some saw Christianity, with its ritual of baptism, as a mystery religion. None of these are "esoteric" in the scholarly sense. The terms "Gnosticism" and "Gnosis" refer to a family of religious movements which claimed to possess secret knowledge. Another important movement from the ancient world was Hermeticism or Hermetism. Both of these are often seen as precursors to esoteric movements in the scholarly sense of the word.