Praxus Prime wrote: Personally, I would say it's demons (I do believe in those). I'm a Christian, so I've looked around in the Bible for anything concerning "ghosts", and the best thing I've come up with so far is demons. I don't believe that they can physically harm me, but that they can make their presence known, and are more likely to do so in times of uncertainty or tumult.
The book of Revelation confirms the existence of Hades (during the final day of judgement, when the dead rise again, "...Hades will {open up} also...").
Ancient Greek Myth, in turn, puts potentially ghost-like entities in Hades, tho I leave the final categorization to you, I thought I'd suggest the consideration.
To be stricter with the act of translation, the Greek word for ghost is 'Phantasma' and for spirit is 'Pneuma' (pronounced Pnevma)(Pneumonia is a branch word for both the lungs and the illness, related to the medical concept of life at the time).Spirit, Pneuma and Psyche are seperate parts of the spiritual anatomy in Greece, as Soul,being,will,spirit etc are different in English ("A brook is not a Creek is not a stream is not a River...")
When the spirit of Jesus reappears to his followers, it is strictly designated to be his Pnevma in the Orthodox texts, never his Phantasm. Also, in Orthodox, the Holy spirit is called "To Agio Pneuma". There is no such term or concept as "The Holy Ghost". ("Agio" [Holy] translates to "A" ["Not of"] and "Gaia" ["Earth"]).
The Odyssey places Odysseus/Ulysses in Hades at one point. It doesn't say anything that I remember about spirits per se, just that he finds some people 'Necroi' ("as Dead", "In the state/status/condition/being of Death"). Amongst these are his Mother, who died while he was fighting at Troy and whom he had no idea had passed away, Agamemnon (I think) and Heracles/Hercules.
No real conclusion (tho I have no right to make up your mind for you in regards to a matter as prominent as spirituality,for lack of a better term), but thought I'd mention just in case it puts more structure somewhere for you.
EDIT: Where I type 'Confirms' I intended to type 'Acknowledges'.