What exactly are the "ghosts" that are chased on shows like "Ghosthunters"?

I think that they are spirits of past people who have not found their way yet. If it is evil sounding than it could be a demon finding it’s way into the mess and making things complicated. I’m actually sort of a chicken when it comes to things like these. When I was younger I wanted to see some sort of paranormal activity becuase I liked the thrill of scary things. I mean like when watching a scary movie and such. My brother and I would gather some of our cousins and we would make a copy of a wiggi board and try to talk to spirits. It sounds silly but it was kind of interesting. We never actually expirienced anything. But one day we were at my grandma’s house in the basement trying to speak to spirits and it was dark and only a candle was lit. A couple of minutes after starting the candle when out on its own and that was supposed to be a sighn of a pressence. So we bolted out of there as fast as we could and didn’t tell anyone about it. The next day our mom asked us what we did down there because according to my grandmother all the lights in the basement and the hall were out.