Poya Day is not a single day but a name for any holiday in Sri Lanka that is held to mark a full moon.
A Poya occurs every full moon.
Uposatha is important to Buddhists all around the world, who have adopted the lunar calendar for their religious observances.
Owing to the moon's fullness of size as well as its effulgence, the full moon day is treated as the most auspicious of the four lunar phases occurring once every lunar month and thus marked by a holiday.
