It is the traditional three month "rains retreat" during which Buddhist monks are expected to stay in their own temple to study the Buddha’s teaching as well as meditating. They are not allowed to travel anywhere or revert to being laymen.
Devout people listen to Buddha’s teaching in the morning of the begining of the Lent or
Boun Khao Phansa
According to legend Buddha’s followers did not stop their wandering during the rainy season and people began to complain that they were trampling on the rice fields and worried they might damage seedlings or small creatures in the fields. When the Buddha heard these worries he forbade the monks to leave their temples for three months.
During this time devout people often abstain from alcohol. They pray for assistance and guidance to encourage merit and happiness in their lives. It encourages them to follow the five major Buddhist precepts: don’t kill animals; don’t steal or engage in corrupt acts; don’t commit adultery; don’t lie; and avoid drinking alcohol. Many take time away from work to make merit for deceased relatives. They also offer robes to the monks.
Early the morning of Boun Khao Phansa people prepare donations of food (particularly khaotom, rice, banana or pork wrapped in banana leaves) and necessities like soap, toothpaste and toothbrushes and towels for the monks. Most temples are very busy during this time with people making merit and giving their donations. At the end of these merit-making activities the monks will recite the teachings of Buddha and tell the history of Lent to temple goers. Later in the evening monks, novices and laypeople bring flowers and candles and walk around the central temple three times.
Taak baat, alms offering or donation, in the morning of the begining of the Lent or Boun Khao Phansa
During this three month buddhist lent monks and novices can't leave their monasteries to become lay people and traditionally lay people are not allowed to get married until the end of the Buddist Lent or Awk Phansa.
Lent ends on the full moon in October the Kathin ceremony when monks receive gifts. These are the most usual months for ordination and for men to enter the monkhood for short periods before they marry and are marked by numerous ordination ceremonies.