When you see someone from far away and think that they're attractive, but on closer inspection realize that they are really, *really* not.
This is like Mt. Fuji in Japan--beautiful from far away, but ugly, dirty, cold, and generally uninhabitable once you get close to it.
Also known as the Mt. Fuji Effect or the Fuji-san Effect.
On arriving at a party:
Girl #1: Ooo, that guy's pretty hot.
Girl #2: You think?
But when they get closer:
Girl #1: Oh, no, never mind. Fuji Effect.