What is the definition of allusion?

An allusion is a reference to something – often a historic or literary reference – used in writing to help a reader understand an idea/situation/person on a deeper level.

An allusion is a literary device, a technique used by writers to create a specific style/feel/flow to their work.

An allusion is a brief reference to something – a person, place, thing – that helps a reader to understand the scene/context better. It calls upon the reader's knowledge of history, literary references, famous people and places in hopes that the reference will do a good job of illuminating what the writer is hoping to express.

Examples:

• "He's a real Romeo, that guy!" (This is an allusion to Romeo from Romeo and Juliet who is known as a real romantic. The reference is supposed to allow the reader to quickly understand the character's style)
• "Let's not open the safe quite yet. Could be a real Pandora's box." (This allusion to the Greek myth, Pandora's Box, implies to readers that whatever is in the safe might be full of secrets that will lead to bad consequences)