1. an arrangement of slow-burning fireworks forming a design or composition when lighted.
2. Theat.a piece of scenery used as part of a stage set, as a profile or three-dimensional construction built to stand independently on the stage floor: A few set pieces simulating rocks and a fence constituted the scenery for the first act.
3. a work of art, literature, music, etc., having a prescribed thematic and formal structure: the set pieces of Restoration comedy.
4. a scene, action, or the like, having a conventional form and functioning as part of the structure of a work of art, literature, etc.
5. a military operation carried out according to a rigid plan.
6. (in a novel, narrative poem, or the like) a passage more or less extraneous to the sequence of events, introduced to supply background, color, or the like.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.