Irony is, in general, when something different than what you expect happens. There are three main types of irony in literature. Here are the three types:
Verbal Irony- This is when a statement seems to contradict itself. An oxymoron (“jumbo shrimp”) is one example.
Situational Irony- When something happens in a story that is the opposite of what you expect, or very different from what is expected, that is situational irony. For example, imagine that a story describes a group of children are approach a house covered in cobwebs, creeping along, and they open the door and suddenly- it turns out to be their own house.
Dramatic Irony- When the reader knows something that the characters in the story don’t, that’s dramatic irony. For example, consider that in the story with the haunted house the children are scared, and we know that it is actually a friendly little old lady living inside. You can imagine that potential for dramatic irony!