According to Wikipedia (the most reliable disource of information I've yet to encounter) the Occult (from the Latin word occultus "clandestine, hidden, secret") means "knowledge of the hidden." It also describes a number of magical organizations or orders, the teachings and practices taught by them, and to a large body of current and historical literature and spiritual philosophy related to this subject. Well, that's close enough for me. But how far back does all this spooky stuff go? When did they start spelling "magic" "magick"?
My occult horror thriller The Book of Paul goes into great depth tracing the subject from the origins of Hermeticism in ancient Egypt and Greece, how the tradition was adopted and expanded on by Greek philosophers like Pythagorus and Plato, how it eventually merged with Gnosticism and Gnostic Christianity--and all those fun book burnings that followed! But for all you curious types who like a good bullet point slide show, here's a few thousand years of arcane history in the time it takes to invoke a lower demon!