Wan Khao Phansa [วันเข้าพรรษา: wan kâo pan-săa] is a period of three lunar months during the rainy season when monks are required to remain in one particular place or temple [วัด: wát]. This year it runs from July 31st to October 27th 2015 (Wan Awk Pansa : วันออกพรรษา).
This tradition originates from old times when Buddha stayed in temples during the rainy season to avoid killing insects or harming the growing seeds. It is a period for study, meditation and teaching of new monks. The monks are allowed to go out during the day but they must sleep in the same temple every night during these three months.