The definition of "allusion" is a brief, usually indirect reference to another person, place, or event—real or fictional. Its use is a shortcut way of bringing extra meaning, clarity, or further explanation of an idea by referencing something that the audience already understands. Allusions may be historical, mythological, literary, pop cultural, or even personal. They can show up in literature, movies, television, comic books, video games, and ordinary conversations.

Key Takeaways: Allusions

The "Oxford Dictionary of Reference and Allusion" explains the technique's use this way:

An allusion is more subtle than a metaphor or simile, as a comparison.

As a verb, the word is allude and as an adjective, allusive. It is also known as an echo or a reference.

Allusion in Literature

Poetry often contains allusion, as every word in a poem carries lots of weight, so a simple allusive phrase in a poem can bring forth many additional layers of meaning. Prose and drama can carry allusions too. Rich sources of allusions include the literary works of Shakespeare, Charles Dickens, Lewis Carroll, and George Orwell (among many others).

Literary works can refer to other works to make a point (like Shakespearean characters referring to Greek myths or common superstitions of the time), or pop culture can make allusions to famous literature. Call someone a Shylock or a Romeo, and you're referring to Shakespeare. Use the phrase "catch-22" to describe a paradoxical situation, and you're actually referring to a novel by Joseph Heller, whether you realize it or not. If someone refers to an Adonis or an odyssey, those are Greek allusions. If you talk about taking the road less traveled, you're alluding to a Robert Frost poem.

Biblical Allusions

Biblical allusions are everywhere because they're so widely understood. Anytime anyone speaks of Noah, a flood, an ark, Moses, a prodigal son returning, money-changers, Adam and Eve, a snake (or serpent), Eden, or David conquering Goliath—those are all biblical allusions. 

Warren Buffet was once quoted as saying, "I violated the Noah rule: predicting rain doesn't count; building arks does."

Allusion in Political Speech

Politicians make allusions all the time. Anytime you hear versions of anyone "speaking softly" or "carrying a big stick," or having a "big stick policy" that person is alluding to Theodore Roosevelt's views on foreign policy or his breaking up monopolies. Another phrase often alluded to is one from John F. Kennedy's inaugural address, "ask not what your country can do for you—ask what you can do for your country."

Or Abraham Lincoln—anytime people are counting in "scores," they're likely alluding to the Gettysburg Address, which starts "four score and seven years ago." The location of Martin Luther King Jr.'s "I have a dream" speech being by the Lincoln Memorial was no accident but an allusion.

Also, widely used allusions to famous quotes include the U.S. Constitution's "We the people" or the Declaration of Independence's "unalienable rights."

Allusion in Pop Culture and Memes

Pop culture allusions have a shorter shelf life, to be sure, but things that start out on social media do on occasion become part of the mass consciousness. For example, if you hear something referred to as a "challenge," it could likely be referring to doing something seen in a video online—either to raise money for charity, as in the ice-bucket challenge that raised money for ALS, or something that's dangerous, like kids attempting to eat laundry detergent pods. 

Memes that follow big news stories are also allusions. Following the news of the latter "challenge," social media saw lots of memes making fun of the idiocy of anyone who'd even think of eating laundry soap, like "Back in my day, we had our mouths washed out with soap as punishment." It doesn't mention the pod challenge directly but alludes to it.