A ghost is a human soul after the death of its body. Ghosts are incorporeal spirits, able to observe the physical plane, but unable to interact with it and invisible and inaudible to most physical beings.

There are four kinds of ghost.

The most common, sometimes called powerless ghosts, are those who are unable to affect the physical world at all.

Poltergeists are ghosts who can, through effort of will, become corporeal, though still invisible and inaudible.

Shades are ghosts who can, through effort of will, become visible and audible. This has the side effect of allowing them to become invisible to incorporeal observers when they wish it as well- Shades can chose to be seen and heard by the corporeal, the incorporeal, both or neither.

Finally possessing ghosts are those who can seize the bodies of the living from them.

There have been incidents of ghosts exhibiting more than one method of interacting with the living, but this is quite rare and often one of these methods will be somehow limited.

For instance, Anna Smith is a powerful poltergeist, able to become corporeal or incorporeal in less than a second. However, she also has some properties of a shade, being permanently audible but invisible to both the corporeal and the incorporeal.