irony
in
Flowers for Algernon -- Novel
(Edited)

when what happens is very different than what might be expected; or when things are together that seem like they don't belong together -- especially when amusing or an entertaining coincidence

This is sometimes referred to as "situational irony."  The term is especially appropriate when actions have consequences opposite to those intended.

The expression ironic smile, generally references someone smiling at situational irony.

All forms of irony involve the perception that things are not what they might seem.

saying one thing, while meaning the opposite or something else -- usually as humor or sarcasm

This is sometimes referred to as "verbal irony." Typically, the speaker says one thing but means the opposite, and the tone of voice or the context of the situation makes the true, contradictory meaning clear.

All forms of irony involve the perception that things are not what they might seem.

When the meaning of a situation is understood by one person, but not by another—especially when a reader or audience knows what characters of a story do not, as in Romeo and Juliet

All forms of irony involve the perception that things are not what they are said to be or what they seem.

Less commonly, Socratic irony is where someone pretends ignorance to get another to think through a problem. This is named after the Socratic method of teaching.

Less commonly still, some also refer to romantic irony as when an author reminds the audience that the fictional words is the author's creation and will play out as the author desires.