A prophecy is a prediction of an event that is yet to unfold.
In Greek Mythology, many prophecies carry many similarities: they foretell terrible events and those who will be affected by the event will try to prevent it from happening, but in doing so set in motion the events of the prophecy.
In the original God of War games, it was foretold that a "marked one" would bring about the destruction of Olympus. To prevent this, Zeus sent Ares and Athena to capture Deimos, whom Zeus believed was the marked one. However, this would in turn cause Kratos, the real marked one, to eventually despise the Olympians and go about seeking their destruction.