A picture or bas-relief made of two panels hinged together, often an altarpiece. Also, any picture consisting of two individual surfaces. Also, an ancient Roman or early Christian two-hinged writing tablet, or two ivory memorial panels.

A three-paneled artwork is a triptych. A four-paneled one is a quadriptych. An artwork of multiple panels — any number greater than three — is a polyptych. (Artlex.com)

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