A painting, usually on hinged panels, often used as an alter piece, invariably small in size and portable.
Here’s a brilliant example:
The Wilton Diptych (c. 1395–1399) depicting King Richard II being presented to the Virgin Mary and Christ by John the Baptist and two English kings (Edward the Confessor and Edmund the Martyr). Painted on hinged panels each 53 x 37 cm.
The painting is an outstanding example of the International Gothic style. Artist unknown.
Currently showing at the National Galley are Scenes from the Lives of the Virgin and other Saints (National Gallery) and Scenes from the Life of Christ (Galleria Nazionale d’Arte Antica, Rome), a reconstruction of what has long been regarded as a diptych painted by Giovanni da Rimini, the most talented artist in 14th-century Rimini.