As expressed in the Sanskrit and translated literally into Tibetan, the term means “to dwell near.” The term comes from the older Vedic traditions in which during full moon and new moon sacrifices, householders would practice abstinence in various forms such as fasting and refraining from sexual activity. These holy days were called upavasatha days because it was said that the gods that were the recipients of these sacrifices would “dwell” (√vas) “near” (upa) the practitioners of these sacrifices. While sacrificial practices were discarded by Buddhists, the framework of practicing fortnightly abstinence evolved into the poṣadha observance, and in fact the term poṣadha is etymologically related to the term upavasatha. See Dutt (1962), p. 73.

A fast or related observance undertaken during the full or new phase of the moon. The Buddhist Hybrid Sanskrit term poṣadha was derived from the classical Sanskrit term upavasatha and translated into Tibetan both as gso sbyong and as bsnyen gnas, i.e. the monastic restoration rite and the eightfold observance both lay and monastic Buddhists may do on the upavasatha.