Basic definition: work of art which is divided in three sections. Usually the middle one is the largest, flanked by two smaller ones.
Arises from early Christian art and was a popular standard format for altar paintings. Outside the context of an altarpiece form some of the best-known triptych works have been created by Hieronymus Bosch, Max Beckmann, and Francis Bacon.
Triptych in literature is used mostly for poetic and short fiction and dramatic forms.
Examples of triptych in bulgarian literature, some which I have read 😀 :
Elisaveta Bagryana – „Юг“, Vladimir Bashev – „Триптих за Пловдив“, Nikolai Haitov – „Пътеки“
Hieronymus Bosch – The Garden of Earthly Delights
The pioneer (painting) – Frederick McCubbin
a free selector and his family making a life in the Australian bush