Wan Ok Phansa (วันออกพรรษา) literally means the “Rains Retreat Exit Day”. This religious holiday marks the end of the Buddhist Lent period in Thailand. Wan Ok Phansa falls every year on the 15th day of the waxing moon of the 11th lunar month. In 2023, it is celebrated on October, 29th, the first day of the Buddhist Lent period (Wan Khao Phansa) having been celebrated on August 2nd.
The end of Buddhist Lent also is known as Maha Pavarana Day (วันมหาปวารณา), which means that it is a time where monks can offer admonitions and helpful advice to other monks. This often comes in the form of older monks offering corrections to younger monks, based on what they witnessed over the last 3 months, but it also can involve the pointing out of mistakes that older monks may have made (though this kind of correction obviously occurs much less frequently).
While Wan Ok Phansa marks the end of Buddhist Lent (aka Vassa), the monks cannot leave the temple yet until the next morning. The following day they can leave the temple at their leisure to preach the dharma, serve the community, and do other traveling, without seeking the permission of the abbot — although many may still do so, depending on their responsibilities at the temple.
On the morning of Wan Ok Phansa, Thai villagers visit their temple to offer food and alms to monks, engage in other merit making activities, and listen to sermons delivered by monks at the temple. Many Thais abstain from drinking alcohol (and some go vegetarian) during the Buddhist Lent. Every year some decide to quit drinking and eating meat altogether after having abstained for 3 months, while others will resume drinking alcohol and eating meat now that the Lent period is over.