I-Think Existence: noun. The particular type of existence a young child gives to the inhabitants of his imagination.
A little philosophy course refresher: Philosopher Rene Descartes made the famous statement, "I think, therefore I am." Believe it or not, what he was saying with that statement is that if he is thinking, there must be someone there doing that thinking, therefore he exists.
Young children, though, seem to take this idea to levels that would shock Descartes. They go beyond "I think, therefore I am," to "I think it, therefore it exists." But what is it? Anything from polka-dotted dinosaurs to closet monsters.
When I was very young, I believed there were hands under the bed that would reach out and grab you if you stepped too close. Why? I have no idea, but to me they had this sort of twilight existence, merely because I thought of them. If my parents told me that there wasn't anything there, I wouldn't have thought they were lying, but I still would have stayed away from the edge of the bed.
As a side note, I began to get over this fear when one night I had a dream that has stayed with me all this time. In the dream, I just got sick of these hands and their nonsense, and decided I would tell my mother about them. As I stood up and began to walk past the bed, a hand reached out and grabbed my ankle. Frustrated and in no mood to deal with this sort of thing anymore, I slapped the hand and it immediately released. Take that!