It also marks the beginning of the Kathina (Kahtein in Burmese) season, during which monks are offered new robes and alms.
The festival’s origins predate the introduction of Buddhism to Burma, and are believed to stem from the Kattika festival, which honors the guardian planets in Indian astrology.
Robe-weaving competitions to weave special yellow monk robes called matho thingan are also held throughout the country, most notably in Yangon’s Shwedagon Pagoda. During these competitions, held for two consecutive nights (the night preceding and the night of the full moon), contestants work nonstop from night until dawn to weave these garments. The tradition commemorates a widely known story of the Buddha’s life. Seeing that the Buddha would soon renunciate, the Buddha’s mother, Maya, who had been reborn in the Tavatimsa heaven, spent the entire night weaving yellow monk robes for him. Her sister Gotami (Buddha’s aunt) continued this tradition and offered new robes annually.
In many parts of Myanmar, hot air balloons lit with candles, are released to celebrate the full moon day, similar to Yi Peng celebrations in Northern Thailand. The balloons are released as an offering to the Sulamani cetiya in Tavitisma, a heaven in Buddhist cosmology and home of the devas, or as a way to drive away evil spirits. Among Tazaungdaing festivals, Taunggyi’s hot-air balloons and firework-launching competition is the most prominent festival. The origin of Taunggyi’s hot-air balloons contest dates back to 1894, when the British first held hot air balloon competitions in Taunggyi, soon after the annexation of Upper Burma.
Alms-giving and charity, both religious and secular, including satuditha feasts, are also commonly undertaken during this festival, as a means of merit-making.
In Burmese tradition, during the full moon day of Tazaungmon, Burmese families pick Siamese cassia buds and prepare it in a salad called mezali phu thoke or in a soup.
According to Wikipedia.