What is "pavarana"

Pavarana is a Buddhist holy day celebrated on Aashvin full moon of the lunar month. It marks the end of the 3 lunar months of Vassa, sometimes called "Buddhist Lent." This day marks the end of the rainy season in some Asian countries like Thailand, where Theravada Buddhism is practiced. On this day, each monk ( Pali: bhikkhu) must come before the community of monks ( Sangha) and atone for an offense he may have committed during the Vassa.

Most Mahayana Buddhists do not observe Vassa, though many Son/Thien monks in Korea and Vietnam do observe an equivalent retreat of three months of intensive practice in one location.