A triptych (pronounced: trip-tick) is a picture in three parts.
The triptych can be used for altarpieces, with a large central panel and two smaller panels painted inside folding doors. As well as being functionally appropriate, the three-fold nature reflects the religious symbolism of the number three.
The passage of time or a story-telling narrative can also become evident in the triptych format, with the panels representing a beginning, a middle and an end.
Although the ways an artist can use the three panels of a triptych vary, there usually will be a strong sense of visual coherence. Be it flowing together to form a single unified scene, or functioning as separate paintings. A continuous horizon line or background, a unified palette, consistent handling of the subject matter, or a progression or continuity of theme or subject are just several ways to achieve this.
The word triptych has its origins in the Greek 'triptykhos' meaning three-layered.