Ghosts

In General
A ghost is the spirit of a deceased person that for some reason or another was unable to pass on to the next life, or who's rest had been disturbed. Ghosts are neither good nor evil has there behaviour is ultimatly dictated by who they where in life and how they died. There are genrally three ways to defeat a ghost; the first is to salt and burn the bones which is used on violent spirits, the second can be helping a ghost resolve its issues which can be used to help benevolant spirits, while the third can be an external element which can include magic that can be used to hold a ghost on the earth plane against it's will.

Types
There are many diffrent types of ghosts in Supernatural which are ceated through the methods of deaths that happen. They include;

Violent spirits
Generally the ghosts of violent people or people who died violent deaths. They are the most dangerous type of spirit and will attack anyone that reminds them of there deaths.

Death Omens
While they apear violent and intimidating they are not dangerous ghots but rather trying to warn people who may be murdered by the person who killed them. They are tied to the earth because they wish to find out who killed them.