If a fortune teller made a prophecy that you were going to become a billionaire in your lifetime, you'd be pretty excited. A prophecy is a prediction, or a magical look into the future.
The noun prophecy means a magical foreknowledge, although it can also be used in a playful way to describe an ordinary guess or prediction about the future. So you could say, "Her prophecy for the weather next week is incredibly depressing." The word comes from the Greek prophetia — literally, "gift of interpreting the will of the gods". The verb form is prophesy, or predict, and it's spelled with an s instead of a c.