Occult is a term that refers to the pratcitioning of Babylonian Witchcraft or any of its Pagan offshoot traditions, including the direct worship of Lucifer in things like Freemasonry and Satanic worship.
Occult practices have been around since at least the time of King Nimrod and Queen Semiramis of Babylon. It's origins are in worship of the sun, something that Lucifer was able to convince man to worship very easily as the benefits of the sun are very obvious. Today, the Nazi Party worships the Black Sun as it's ultimate higher power.
The term occult can encompass a wide variety of people participating in the Satanic Hierarchy and Paganism in general.