There are several forms of irony, all commonly used by writers and performers.
Irony can be humorous or tragic, and often both. When irony is used, the reader or audience will often feel ‘in on the joke’, usually to the exclusion of others involved: something is communicated that is different from what is being said, or is happening.
Verbal irony
Verbal irony (spoken or written) is a phrase that states something other than the evident truth, creating a ‘gap’ between what the speaker is saying and what the listener understands is really being said. Often it will be used to emphasise or make light of an undesirable situation.
Sarcasm
Sarcasm is a variant of verbal irony. It is characterised by a bitter, unemotional tone and is often intended to make the person at whom it is directed feel bad.
Situational irony
This is where the reader senses a contrast between something that might be expected to happen and what actually happens, either in real-life or fiction. The reader will often feel this reveals a truth. Its effect may be funny, tragic or both.