An allusion is when a person or author makes an indirect reference in speech, text, or song to an event or figure.
Often the allusions made are to past events or figures, but sometimes allusions are made to current famous people or events.
The allusion does not give much detail about the reference-it does not describe things in detail. Rather, because these events are momentous-significant historically, culturally, or politically-the speaker or author expects that people in general would understand the allusion without explanation.
Allusions are often used within a metaphor or simile. The comparison alludes to an event or person of significance that everyone should understand.
Allusions often make reference to previous works of literature, especially references to the Bible and Greek or Roman mythology.