is there really a ghost?

Yes there is, but you did not mention in details what kind of ghost or spirit because there are many kind of spirit; there is called the spirit of God, and also the spirit of satan, there is also Ghost from supernatural belief but the latter is delusion or maybe an associated of bad spirit which coming from satan. Now if you are referring to the movie "ghost", it was only a representation of how the Ghost works but in real life, the ghost cannot be seen.