Vesak Day: Vesak Day (known also by the names of Wesak Day, Buddha Purnima, or Buddha Day) is commonly regarded as the most important Buddhist holiday in Southeast Asia and in the Theravada and Tibetan traditions. It commemorates three events: the birth of Siddhartha Gautama, the man who became the Buddha; his Enlightenment (Nirvana); and when he died and passed into parinirvana (meaning “nirvana-after-death” in Sanskrit).