Vesak (Vesākha; Vaiśākha), also known as Buddha Jayanti, Buddha Purnima, Buddha Day, and Phật Đản, is a holiday traditionally observed by Buddhists in South Asia and Southeast Asia, as well as Tibet and Mongolia. It is the most important Buddhist festival. The festival commemorates the birth, enlightenment (Nibbāna), and passing (Parinirvāna) of Gautama Buddha in Theravada, Tibetan Buddhism and Navayana.
The name Vesak is derived from the Pali term vesākha or Sanskrit vaiśākha for the lunar month of Vaisakha, which is considered the month of Buddha's birth. In Mahayana Buddhist traditions, the holiday is known by its Sanskrit name (Vaiśākha) and derived variants of it.
In the East Asian tradition, a celebration of Buddha's Birthday typically occurs around the traditional timing of Vesak, while the Buddha's awakening and passing away are celebrated as separate holidays that occur at other times in the calendar as Bodhi Day and Nibbāna Day. In the South Asian tradition, where Vesak is celebrated on the full moon day of the Vaisakha month, the Vesak day marks the birth, enlightenment, and the ultimate passing away of the Buddha.
Although Buddhist festivals have centuries-old tradition, the first conference of the World Fellowship of Buddhists held in Sri Lanka in 1950 formalized the decision to celebrate Vesak as the Buddha's birthday across multiple Buddhist countries. The resolution that was adopted at the World Conference reads as follows:
That this Conference of the World Fellowship of Buddhists, while recording its appreciation of the gracious act of His Majesty, the Maharaja of Nepal in making the full-moon day of Vesak a Public Holiday in Nepal, earnestly requests the Heads of Governments of all countries in which large or small number of Buddhists are to be found, to take steps to make the full-moon day in the month of May a Public Holiday in honour of the Buddha, who is universally acclaimed as one of the greatest benefactors of Humanity.