A ghost is the spirit of a deceased sentient creature. Ghosts are incorporeal in nature and are only vulnerable to silver weapons when they are in the land of the living. They exist on the border of the two planes, the dream plane of the dead and the primordial plane of the living.
A ghost's spirit is bound to a body of water, where the veil between the dreaming and waking world is at it's thinnest. These water bodies are called haunts, and a ghost's connect to the primordial plane gets severed when these haunts dry out, but after the water returns so will the ghost after a few days. Ghosts can be a repetitive nuisance for those who live near one of their haunt.
Ghosts can also be controlled of wizards, sorcerers, warlocks, etc. In this case the ghost will finally be put to rest when destroyed on the primordial plane or the master of the ghost dies. It is very uncommon for this to happen as it is frowned upon by the Hilalian school of Necrotic Powers to bind an incomplete sentient being to your service. A ghost's weapon of choice usually consists of whatever weapons they preferred to carry in their mortal life, and maybe a spell or two if they were a wizard or sorcerer.