Auspicious for all good work: charity, marriage, religious rites, the Satyanarayana observance and the full-moon fast. Purna class, and the strongest tithi of the bright fortnight.
Meaning
Purnima is the fifteenth tithi of the waxing fortnight, the full moon, when the Moon stands opposite the Sun and its paksha bala is at its height. It is the Purna tithi of the bright fortnight and the day of the full-moon observances, and its adhidevata is Vishnu (with Chandra, the Moon, in some lists).