A triptych (rhymes with cryptic) is a painting or carving
consisting of three separate canvases or panels meant to be displayed
as a group.
The term comes from the Greek triptychos, ‘having three
folds,’ a word both the ancient Greeks and Romans employed
to refer to a hinged writing tablet made of three panels.
Medieval and Renaissance artists used this hinged, three-piece
format to produce easy-to-transport altarpieces.
Modern artists like Roy Lichtenstein (1923-97) and David
Hockney (b. 1937) have also used the triptych format.
Bonus word: a diptych (DIP´-tik) is a painting or carving
consisting of two panels.