What is a ghost?. Well there are different theories. One is called the tape recorder effect ,this is where a person dies in such a trauma that the event is impregnated into the atmosphere and when someone sensitive enough comes along they then pick up the event on a loop and see a glimpse of the person. Also you have theory that they are living beings our souls surviving after the physical dies. Both are true the first does not interact where the second does,thats how you tell the difference. Happy hunting!