the use of words to convey a meaning that is the opposite of its literal meaning: the irony of her reply, “How nice!” when I said I had to work all weekend.
Literature. a technique of indicating, as through character or plot development, an intention or attitude opposite to that which is actually or ostensibly stated. (especially in contemporary writing) a manner of organizing a work so as to give full expression to contradictory or complementary impulses, attitudes, etc., especially as a means of indicating detachment from a subject, theme, or emotion.
an outcome of events contrary to what was, or might have been, expected.