This public holiday in Sri Lanka takes place on the full moon day of Vap, the seventh month in the Sinhalese calendar. It usually falls in October in the Western calendar.
The festival Marks Buddha's preaching of Abhidamma to the gods in Tavatimsa and the end of the Buddhist period of fasting.History of Vap Full Moon Poya
Maya, the mother of Buddha died a week after Buddha was born. She was reborn in the celestial abode of Tavatimsa as a god named Santusita. To honour his mother, Buddha ascended to the Tavatimsa Heaven and preached from the Abhidamma texts to Santusita for three months.
Buddhist Lent begins on Esala Full Moon Poya (July) and lasts for three months. During this time, Monks will stay inside their temples and rely on alms from devotees. The full moon in Vap marks Buddha's return to earth and signifies the end of Buddhist Lent.