Foreshadowing is a literary resource in which the author tells the reader or audience about certain developments in the argument that may occur later in the story. It is mostly used to mentally prepare the reader to process the development of the story.
In Oedipus the King, Sophocles uses foreshadowing to show the reader that horrible things will happen since Oedipus fulfilled his prophecy (without knowing it) by killing his father and marrying his mother. The character of Teresias, the prophet, is important in the construction of foreshadowing, in addition to the meaning of the name of Oedipus ("swollen foot"). According to the legend, before being adopted, Oedipus suffered injuries to his feet, causing him to swell.