Esoteric
Esoteric (Greek esōterikós, inner) refers to knowledge that is internal, accessible only to initiates of a tradition. Opposed to exoteric (external, public). The term gained current meaning in the 19th century as the umbrella name for occultism, theosophy, hermeticism, alchemy, Kabbalah, etc.
Esoteric vs occultism
Often used as synonyms, but technically: esoteric is the broader category (initiatory knowledge); occultism is the 19th-century Western movement (Eliphas Lévi, Papus, Helena Blavatsky) that systematized esoteric knowledge for the modern world.