Poṣadha

poṣadha (布薩). Nurturing purity, a mandatory system for monastic Buddhists to convene twice each lunar month on poṣadha days (布薩日), new-moon and full-moon days, in designated places for different groups, to disclose their transgressions, repent of them, and listen to a qualified member recite the precepts. When lay Buddhists choose to accept and observe the eight precepts on one or more of the six purification days during a lunar month, it is also called poṣadha.

Source

www.sutrasmantras.info