An allusion is a reference to a statement, a person, a place, or an event from various fields such as literature, history, religion, mythology, politics, sports, science, or pop culture. It is a way of indirectly referring to something by mentioning it briefly, allowing the reader or listener to make connections and understand the deeper meaning or significance behind it. Allusions add depth and complexity to a piece of writing or conversation by drawing upon shared cultural knowledge and associations.