Irony is when -

♦ Irony:
- A statement or a situation or an action which actually means the opposite of its surface meaning.
- Irony is when there are two contradicting meanings of the same situation, event, image, sentence, phrase, or story. In many cases, this refers to the difference between expectations and reality.

• The first sentence of Pride and Prejudice is an example of irony:
“It is a truth universally acknowledged, that a single man in
possession of a good fortune, must be in want of a wife.”

• This line from Samuel Coleridge’s “Rime of the Ancient Mariner” describes the dark irony of a sailor dying of thirst on his boat while he is surrounded by water.

Source: An ABC of English Literature - Dr M Mofizar Rahman and literaryterms.net