The term irony is derived from a Greek word that means "one who dissembles." There are three important types: verbal, dramatic, and situational. Each signals a difference between appearance and reality.
Verbal irony involves figures of speech, in which what is said is not what is meant. There are several kinds:
Sarcasm: In sarcasm, the speaker means the opposite of what is said. Suppose someone walks out the door in the morning, hoping for sunshine, and finding sleet and freezing rain exclaims, “What a great day!” This is sarcasm, and irony results because the opposite of what is literally said is what is actually meant. The contempt in this particular kind of sarcasm is for the event described: it is not personal criticism — the speaker is disgusted by the lousy weather.
Equivocation: In equivocation, the speaker says something that is true if understood properly, but at the same time, does everything possible to ensure that it will be misunderstood. This allows a speaker to tell the truth but to avoid revealing certain matters. For example, in Macbeth, Act 2, scene 3, upon hearing Lennox refer to the strange and prophetic events of the previous night, Macbeth responds "'Twas a rough night." He may seem to be simply affirming Lennox's observations, but having seen the discussions surrounding the murder of Duncan, the audience knows that there is another meaning to Macbeth's statement that Lennox cannot understand.
In Dramatic irony, the author, narrator or playwright reveals to the reader or audience information about a character's situation of which the character is not aware. Portents and foreshadowing are two ways in which an author or playwright can accomplish this; another way is by allowing the reader or audience to witness scenes or situations that a character does not have access to. For example, when the audience first sees Macbeth in Act 1, scene 3 of the play that bears his name, and the witches hail him as Thane of Cawdor, they know — but he does not — that the Thane of Cawdor has been condemned to death and his title been designated for Macbeth by King Duncan. For the audience, this happened in Act 1, scene 2, but Macbeth receives the news later, after the prophecy, creating a gap between what the audience knows and what he knows.
Situational irony results when well-founded expectations — either a character’s or the audience’s — appear to be secure but fail to manifest; this is another way in which appearance and reality can wind up in contradiction. Again, Macbeth’s road to keep the throne and overthrow Malcolm’s claim seems certain to him, since "none of woman born shall harm Macbeth," and he is safe until "Birham wood be come to Dunsinane" — two assurances that give him a fair certitude of success. Both of these promises turn out to have been equivocations, however, and his success is by no means assured. In the final scenes of the play, Macbeth's expectations are overturned, and he is killed.
Though irony has a well-established presence in literature and fine arts, it is also a staple of many forms of pop culture. One outstanding example of this is super hero fiction, either in comic books or in movies, which repeatedly use it to twist the plot, creating engaging and dramatic situations. The 1989 film Batman serves as an example in pop culture. In this movie, Bruce Waynes's choice to engage in crime fighting is a direct result of the murder of his parents when he was young. The murderer, at the time a two-bit thug, would later be pushed into a vat of acid by Batman during a robbery of a chemical plant. After plastic surgery and recovering from the acid burns, the two-bit thug reinvents himself as one of Batman's greatest adversaries, the Joker. The irony that each of these two characters are actually responsible for creating their enemy leads to dark, engaging plot lines.