A paranormal investigator is someone who investigates the paranormal world around them. It expands beyond ghost to Big Foot, U.F.O.s and other creatures of the unknown. Matter of fact, the same equipment that is use for ghost hunting can be used to investigate other things.
While I might lean one way or another on the list above when it comes to investigating the paranormal world. I believe in U.F.O.s a lot more than I do in Big Foot because a 9ft hairy ape man would stand out much more today than 25 to 30 years ago due to population growth humans and shrinking of forest.