Allusion is a reference to a person, event, or literary work outside the poem. Allusions are usually implied or indirect, and poems with allusions do not necessarily cite the work or historical event they are referencing. When poets use allusions, they are assuming a shared knowledge between themselves and the reader, therefore readers are expected to understand the poet’s reference.
Traditional Western literature often makes allusions to the Bible and Greek mythology with the understanding that most readers will have experience with the texts. However, some poets used intentionally obscure allusions in their writing, knowing that few readers would understand the references. Allusions can be used to enhance a text by bringing in context or background knowledge. As time progresses, allusions and elements of culture considered common knowledge can change.