Initiation is a rite of passage, ceremony, marking entrance, or acceptance into a group or society. In an extended sense it can also signify a transformation in which the initiate is 'reborn' into a new role.
H. P. Blavatsky wrote:
Initiate. From the Latin Initiatus. The designation of anyone who was received into and had revealed to him the mysteries and secrets of either Masonry or Occultism. In times of antiquity, those who had been initiated into the arcane knowledge taught by the Hierophants of the Mysteries; and in our modern days those who have been initiated by the adepts of mystic lore into the mysterious knowledge, which, notwithstanding the lapse of ages, has yet a few real votaries on earth.
- Helena Petrovna Blavatsky, Theosophical Glossary (Krotona, CA: Theosophical Publishing House, 1973), 156.