It is a good questions, and many don't believe in ghosts, but do beleive in spirits. And furthermore, some say that the term ghost is suppose to mean bad spirits. I know someone said they are "thoughtforms" in action. If this is true, I can say that I have actually been thinking of people, and just as I am finishing the thought of them or perhaps a conversation about them...at times I run into them at a store, food place, etc, etc. I guess all that's coincidence maybe, but maybe that's not what is meant by "thoughtforms" in action as sometimes I am bad about misunderstanding terms at times. Maybe I just notice it more, or maybe the people are just going to the same store as I am. It is weird, but it happens.