Citation:
An allusion is a reference to a well-known person, event, or piece of literature in order to enhance the meaning of a current work. It adds depth and layers of meaning by connecting the present with the past.
Symbolism is when an object or action represents something deeper or more abstract than its literal meaning.
A metaphor is a figure of speech that compares two unrelated things without using "like" or "as."
Irony occurs when there's a contrast between what's expected and what actually happens.