The use of hints and clues to suggest what will happen later in a plot.
It can keep the reader intrigued by giving them subtle hints that make them think that they might be connected to the story somehow. It can also make the ending of a story more surprising if they didn't notice the foreshadowing before.
Example: The Chosen One
This is a clip from Star Wars Episode III, it's the second bit of foreshadowing for the same ultimate event. It references the initial foreshadowing in Episode I about how Anakin is the chosen one. Obi-Wan says that Anakin will now leave the force in darkness, but will eventually bring balance to it.
You were the chosen one!
Example: Batman Begins Ending Scene
This is a not so subtle example of foreshadowing, at the end of batman begins Gordon hands batman a 'calling card' and it's a joker card out of a deck of cards. This is foreshadowing that the next movie is going to be about the joker.
Batman Begins Movie End
Try to find a popular example of foreshadowing that the rest of the class would recognize. Each table shares one example.