Fate is the idea that all of our actions and all resulting outcomes have been predetermined. They are usually controlled by one or more supreme beings. Fate can also be determined by our own previous actions, which is also referred to as determinism. For example, in games where time travel forces you to do certain things in order to prevent a paradox, this is due to the series of events which would be disrupted by the out-of-place occurrence if nothing is done to prevent it. Sometimes fate is not predetermined by supreme beings, but simply exists as a kind of "force" unto itself and it alone drives our actions, similar to the way in which an oracle predicts the actions of the future and the character is doomed to that outcome.
Some games pit the main characters against fate itself or the supreme being(s) who control fate. This usually involves the unwillingness of the character(s) to accept their prescribed fate or to be the puppets of an unseen master.
God of War
The sisters of Fate weave and control the fate of all the beings in the world. Kratos ultimately kills them all off and obtains the powers himself.
Medivh predicts the future and tells the orcs and humans that they must unite against the shadow.
World of Warcraft
A'dal in Shattrah predicts the future battles that the player will face