Vesākha (Pali;Sanskrit: Vaiśākha, Devanagari: वैशाख), Wesak or Vesak, also known as Buddha Purnima and Buddha Day, is a holiday observed traditionally by Buddhists on different days in Sri Lanka, Nepal, Tibet, Bangladesh, Bhutan, India, and the South East Asian countries of Philippines, Singapore, Vietnam, Thailand, Cambodia, Laos, Malaysia, Myanmar and Indonesia, and other places all over the world. Sometimes informally called "Buddha's Birthday", it actually commemorates the birth, enlightenment (nirvāna), and death (Parinirvāna) of Gautama Buddha in the Theravada or southern tradition.
The exact date of Vesak is based on the Asian lunisolar calendars and is primarily celebrated in Vaisakha month of the Buddhist calendar and the Hindu calendar, and hence the name Vesak. In Nepal, which is considered the birth-country of Buddha, it is celebrated on the full moon day of the Vaisakha month of the Hindu calendar, and is traditionally called Buddha Purnima, Purnima meaning the full moon day in Sanskrit.
In Theravada countries following the Buddhist calendar, it falls on a full moon Uposatha day, typically in the 5th or 6th lunar month. In China, Japan, and Korea, it is celebrated on the eighth day of the fourth month in the Chinese lunar calendar. The date varies from year to year in the Western Gregorian calendar, but usually falls in April or May. In leap years it may be celebrated in June.