Irony is like sarcasm: you can say "oh yeah, that sounds SO fun" and mean "that doesn't sound fun at all"
Irony in a situation is when, for example, you do everything you can to prevent something from happening, but your trying to prevent it is what makes it happen.
It is also a literary technique, originally used in Greek tragedy, by which the full significance of a character's words or actions are clear to the audience or reader although unknown to the character.
