Ghosts wear out like old clothes and go on to wherever old ghosts go. The sunken grave would fade away, probably in my lifetime. If I could avoid killer zombies for a few years. And vampires. And gun-toting humans.
Oh hell, the hot spot would probably outlast me.

(The Laughing Corpse, page 117, paragraph 6)

* They are also called hotspots, not exactly an entity, more a source of energy that will eventually fade with time.

* Ghosts have substance only if someone gives them substance. They can grab and hold things, but only if someone pays attention or is frightened by them. If they are ignored, they will slip away.

* Ghosts tend to bear a grudge against the living. They cannot harm a person, but they can scare someone and laugh while they are doing so.

* Sometimes, they are no more than psychic impressions - strong emotions that soak their way into the walls of a building, like a hospital. Almost like an emotional tape recorder - sometimes there are images, sometimes just sound.

* The dead need to buried in a hole that is deep and wide otherwise they get restless and their spirits may come back. However, cremation prevents the creation of ghosts.