A soul trapped on this plane, and considered an undead creature. They have usually died a sudden, violent death or have unfinished business that prevent them from passing on. There are many different kinds of ghost, some can cause physical harm, others can move objects or use spells, and some can possess the living. If they are “killed” (brought to zero hit points) they will often reform over time. They can sometimes be released by various magics or by finishing whatever business held them to this plane.