In literary terms, a conceit is an extended metaphor with a complex logic that governs an entire poem or poetic passage. By juxtaposing images and ideas in surprising ways, a conceit invites the reader into a more sophisticated understanding of an object of comparison.
An often-cited example of the metaphysical conceit is the metaphor from John Donne's "The Flea," in which a flea that bites both the speaker and his lover becomes a conceit arguing for the depth of their union:
In the Renaissance, the term (which is related to the word concept) indicated any particularly fanciful expression of wit, and was later used pejoratively of outlandish poetic metaphors.
Recent literary critics have used the term to mean simply the style of extended and heightened metaphor common in the Renaissance and particularly in the 17th century, without any particular indication of value. Within this critical sense, the Princeton Encyclopedia makes a distinction between two kinds of conceits: the Metaphysical conceit, described above, and the Petrarchan conceit. In the latter, human experiences are described in terms of an outsized metaphor (a kind of metaphorical hyperbole), like the stock comparison of eyes to the sun, which Shakespeare makes light of in his sonnet 130: "My mistress' eyes are nothing like the sun."