Definition of Foreshadowing: 

Foreshadowing is a device whereby a narrator or character hints at later events in the story. Sometimes foreshadowing can be subtle, with clues dropped in that are hard to catch on a first reading. Other times it can be more obvious, like when a character predicts their own death.

Examples of Foreshadowing in Literature:

“‘Enough,’ he said; ‘the cough's a mere nothing; it will not kill me. I shall not die of a cough.’
‘True—true,’ I replied...”
—Edgar Allan Poe’s “The Cask of Amontillado”

“The Cask of Amontillado” is full of foreshadowing, beginning with the first line, which informs readers that it is a tale of revenge. This quoted exchange employs a bit of dark humor to foreshadow the fact that Montresor, the narrator, will kill Fortunato before the cough has the chance.  

“It is a truth universally acknowledged that a single man in possession of a good fortune must be in want of a wife.”
—Jane Austen’s Pride and Prejudice

The very first line of the novel foreshadows the focus of the entire plot: marriage and the conflict between love and pragmatism. Though there are many missteps along the way, all of the single male characters in possession of good fortunes end up with wives: Bingley, Darcy, Collins, and, though he lacks money, Wickham. Essentially, readers are told exactly what will happen before they are even introduced to a single character. 

“But tomorrow I die, and today I would unburthen my soul.”
—Edgar Allan Poe’s “The Black Cat”

By establishing the story as a confessional, Poe foreshadows the ending of the tale by stating that the narrator will die at the end. He does not tell us how or why, both of which will become clear as the story unfolds, but he offers this dramatic foreshadowing to hook readers into the story.