What does it mean when you dream of your dad and a ghost?

Without further information, it is difficult to suggest any interpretation. It would make a difference what your dad and the ghost are doing; for example, a dream of your dad fighting a ghost would have a different meaning from a dream where he is just standing around with a ghost hanging nearby... or dancing... or singing... or whatever. The emotions you experience during the dream are also important and make the difference between a nonsensical dream and a terrifying nightmare.