anachronism

Reference of an event, custom, or expression to a wrong date, common in literature, painting and other forms of art.

Anachronism is often deliberately adopted as a device in order to emphasize the strengths and weaknesses of either the misplaced object or of the period it has been placed into. Sometimes, its purpose is merely for comic relief, as The Hitchhiker's Guide to the Galaxy (1979) by Douglas Adams. In science fiction, time travel provides vast scope for anachronism. The film Back to the Future (1985) puts it to both comic and serious use.