Anachronism is a literary term describing an object that appears in a time period it logically shouldn't.
An anachronism in Shakespeare's Julius Caesar was a mechanical clock, which did not exist in the time in which the play was set.
In serious film or drama, any anachronisms that appear tend to be the result of mistakes or oversights on the part of the producers. For example, historical dramas on television are often marred by anachronistic modern turns of phrase that sit uneasily with the time period in which they are set. In comic productions, blatant anachronisms can be a good source of humor if used judiciously, surprising the audience and sending up dramatic conventions. This often happens in pantomime, where, for example, characters who are supposedly living in pre-industrial English villages may suddenly begin debating the visual appeal of modern-day celebrities such as Tom Cruise.