Irony is a juxtaposition of what, on the surface, appears to be the case with what is actually or expected to be the case. Originally a rhetorical device and literary technique, irony has also come to assume a metaphysical significance with implications for one's attitude towards life.
The concept originated in ancient Greece, where it described a dramatic character who pretended to be less intelligent than he actually was in order to outwit boastful opponents. Over time, irony evolved from denoting a form of deception to, more liberally, describing the deliberate use of language to mean the opposite of what it says for a rhetorical effect intended to be recognized by the audience.