What is irony?

a literary technique that involves surprising, interesting, or amusing contradictions
a progression of thoughts, a sequence of events, or a building of an argument within a poem
a unit of meaning in poetry
a paraphrase of a stanza of poetry

Irony is:
A. a literary technique that involves surprising, interesting, or amusing contradictions. 

The definition of irony is: a state of affairs or an event that seems deliberately contrary to what one expects and is often wryly amusing as a result.

An example of irony would be that the name of Britain’s biggest dog (until it died recently) was 'Tiny'.