Poya Days
Sri Lankan Poya days are monthly Buddhist holidays that commemorate events in the life of Lord Buddha. There are 12 Poya days in a year, with each one dedicated to a specific event. These days are significant in Sri Lankan culture and are observed with religious activities and ceremonies.
Uposatha
An Uposatha (Sanskrit: Upavasatha) day is a Buddhist day of observance, in existence since the Buddha's time (600 BCE), and still being kept today by Buddhist practitioners. The Buddha taught that the Uposatha day is for "the cleansing of the defiled mind," resulting in inner calm and joy. On this day, both lay and ordained members of the sangha intensify their practice, deepen their knowledge and express communal commitment through millennia-old acts of lay-monastic reciprocity. On these days, the lay followers make a conscious effort to keep the Five Precepts or (as the tradition suggests) the ten precepts. It is a day for practicing the Buddha's teachings and meditation.
Observance Days
Depending on the culture and time period, Uposatha days have been observed from two to six days each lunar month.
Theravada countries
In general, Uposatha is observed about once a week in Theravada countries in accordance with the four lunar phases: the new moon, the full moon, and the two quarter moons in between. In some communities, such as in Sri Lanka, only the new moon and full moon are observed as Uposatha days.
Mahayana countries
In Mahayana countries that use the Chinese calendar, the Uposatha days are observed ten times a month, on the 1st, 8th, 14th, 15th, 18th, 23rd, 24th, and the final three days of each lunar month. Alternatively, one can observe Uposatha days six times a month, on the 8th, 14th, 15th, 23rd, and the final two days of each lunar month. In Japan, these six days are known as the roku sainichi (Six Days of Fasting).