A period piece is a work of art set in, or reminiscent of, an earlier time period.
In the performing arts, a period piece is a work set in a particular era. This informal term covers all countries, all periods and all genres. It may be as long and general as the medieval era or as limited as one decade—the Roaring Twenties, for example.
Harold Bloom in The Western Canon (1994) labels those works not included in his list of 20th century "classics" as being mostly "period pieces" (see Appendix header for "The Chaotic Age"). Since these works are still being widely read (Harry Potter for example), it is impossible to know if they will become regarded as classics in the future or simply fade away into mostly unread period pieces.