Most times that people talk about "ghosts", they should really consider that there is no such thing. There are, however, many demons who pretend to be ghosts, and this is when people go astray. The spirit of a recently deceased person may linger for a day or so, but then they must go on to visit other places for forty days, at which point they are assigned their eternal home. So if someone has been gone for a year, say, and their "ghost" appears, you can be sure it is a demon. Do not try to communicate with the demon. It is much smarter than you.