This upcoming December 8th is Bodhi Day or The Buddha’s Enlightenment. Bodhi Day is not as popularly celebrated as Wesak Day, the Birth of the Buddha, however, it is still observed in many mainstream Mahayana traditions including the Zen and Shin Buddhist schools, where it is known as Rohatsu.
Among the Mahayana Buddhists, this holiday celebrates the Buddha’s attainment of Nibbana. Which is the understanding of the truth of existence, freeing himself from all human suffering, and finding perfect happiness.
The date, 8th December, is based on the Japanese Buddhist calendar but Buddhists elsewhere celebrate it on different days.
During this holiday there are many retreats some lasting for 10 days. In general the retreat ends on Bodhi day.