Definitions for "Dramatic Irony"
situation where a character is unaware of something the audience knows
plot device in which a character holds a position or has an expectation that is reversed or fulfilled in a way that the character did not expect but that we, as readers or as audience members, have anticipated because our knowledge of events or individuals is more complete than the char-acter's.
The situation when the audience knows something the characters don't, as in Shakespeare's Macbeth, when King Duncan remarks on his inability to judge character - while warmly greeting the man (Macbeth) we already know plans to assassinate him.