triptych - A painting or carving that has three side-by-side parts, panels, or canvases. Typically, a triptych has three hinged panels, the two outer panels designed so that they can be folded in towards the central one.
This was a common form for an altarpiece during the Middle Ages and the Renaissance. The outer parts of such triptychs were typically hinged to the central one so that they could be closed over it, and in this case reverse sides were often painted.
A triptych can also be, more loosely, something composed or presented in three parts or sections.
"Triptych" has come to us from the Greek "triptychos," formed by combining "tri-" ("three") and "ptyche" ("fold" or "layer"). Although "triptych" originally described a specific type of Roman writing tablet that had three hinged panels, it makes sense that the word was adopted first for a three-paneled painting, and then to include anything composed of three parts. "Triptych" can even be used as a synonym for "trilogy."
The related modern word "trifold" is popularly used to describe a common brochure format with two and three folds; or three hinged boards for museum, educational, commercial, and other displays.
A two-paneled artwork is a diptych. A four paneled one is a quadriptych. An artwork of multiple panels is a polyptych.
A painting with four or more panels might be a screen, if only because it is comparable to a screen, even if it doesn't function as one.
Bernardo Daddi (Italian, Florentine, about 1280-1348), Triptych: Madonna, Saint Thomas Aquinas, and Saint Paul, about 1330, tempera and gold leaf on wood panel, 47 1/2 x 22 inches (120.7 x 55.9 cm), J. Paul Getty Museum, Malibu, CA.
Joos van Cleve and a collaborator (Netherlandish, active by 1507, died 1540/41), The Crucifixion with Saints and a Donor, triptych, c. 1520, oil on wood; shaped top: central panel, painted surface 38 3/4 x 29 1/4 inches (98.4 x 74.3 cm); each wing, painted surface 39 3/4 x 12 7/8 inches (101 x 32.7 cm), Metropolitan Museum of Art, NY.
Max Beckmann (German, 1884-1950), Beginning, 1949, oil on canvas, 69 x 125 1/2 inches (175.3 x 318.8 cm), Metropolitan Museum of Art, NY. See Expressionism.
Francis Bacon (English, 1909-1992), Three Figures in a Room, 1964, oil on canvas, 198 x 441 cm, Georges Pompidou Center, Paris. See expressionism.
Elysha _____ (American, contemporary, at 10 years old), Brown and White Dog, from Realistic to Abstract, 2005, colored pencils on paper, 6 x 18 inches. See abstraction and realism, and more children's art of this sort.
Also see Gothic.