See also : Ghosts | Damned | Demons

The technology of hunters allows them capturing supernatural beings, which were called ghosts since the dawn of time. Basically, they are the reflections of the dead people in an alternate dimension affecting the world around us. Up to this day we don't know if ghosts share their dimension with demons, or there are two separate dimensions. If we assume that there are separate dimensions, we also can't be sure if ghosts and demons can travel between them.
There are many types of ghosts. According to the Book of Ghosts by Allan Kardec, ghosts can be divided by taking into consideration their character, their way of interaction with people and groups of people which are affected by them.
As the hunters deal with all kinds of spirits, only the most deadly, and at the same time the most hidden ones, as a separate kind - the Damned.