"The occult (from the Latin word occultus "clandestine, hidden, secret") is "knowledge of the hidden". In common English usage, occult refers to "knowledge of the paranormal", as opposed to "knowledge of the measurable", usually referred to as science. The term is sometimes taken to mean knowledge that "is meant only for certain people" or that "must be kept hidden", but for most practicing occultists it is simply the study of a deeper spiritual reality that extends beyond pure reason and the physical sciences. The terms esoteric and arcane can also be used to describe the occult, in addition to their meanings unrelated to the supernatural.
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.
Occultism is the study of occult practices, including (but not limited to) magic, alchemy, extra-sensory perception, astrology, spiritualism, religion, and divination. Interpretation of occultism and its concepts can be found in the belief structures of philosophies and religions such as Chaos magic, Gnosticism, Hermeticism, Theosophy, Wicca, Thelema and modern paganism. A broad definition is offered by Nicholas Goodrick-Clarke:
OCCULTISM has its basis in a religious way of thinking, the roots of which stretch back into antiquity and which may be described as the Western esoteric tradition. Its principal ingredients have been identified as Gnosticism, the Hermetic treatises on alchemy and magic, Neo-Platonism, and the Kabbalah, all originating in the eastern Mediterranean area during the first few centuries AD.
From the 15th to 17th century, these ideas that are alternatively described as Western esotericism, which had a revival from about 1770 onwards, due to a renewed desire for mystery, an interest in the Middle Ages and a romantic "reaction to the rationalist Enlightenment". Alchemy was common among important seventeenth-century scientists, such as Isaac Newton, and Gottfried Leibniz. Newton was even accused of introducing occult agencies into natural science when he postulated gravity as a force capable of acting over vast distances. "By the eighteenth century these unorthodox religious and philosophical concerns were well-defined as 'occult', inasmuch as they lay on the outermost fringe of accepted forms of knowledge and discourse". They were, however, preserved by antiquarians and mystics.
Based on his research into the modern German occult revival (1890–1910), Goodrick-Clarke puts forward a thesis on the driving force behind occultism. Behind its many varied forms apparently lies a uniform function, "a strong desire to reconcile the findings of modern natural science with a religious view that could restore man to a position of centrality and dignity in the universe". Since that time many authors have emphasized a syncretic approach by drawing parallels between different disciplines."
Basically the occult is anything which is not of God!