About this term
Source: Oxford University Press
Term used to define a picture consisting of three parts and denoting both the object itself and its compositional form. As an object the triptych may vary in size and material, but usually consists of a central panel flanked by wings (or shutters), which may be hinged; as a compositional form it is a tripartite structure, often with an emphasized central element. Although its imagery was, until the 19th century at least, predominantly religious, the object as such was not tied to a specific function.
From Grove Art Online