Saathā upvas (upvas) generally refers to fasting as a form of external austerity in Jain practice. Upvas is one of the main bahya tapa used to stop new karmas (samvara) and shed old karmas (nirjara). It can take several forms, from complete abstention (no food or water) to lighter fasts like Ekasana (one meal) or Beasana (two meals), and special longer vows such as Chauvihar or Athai upvas. The exact rules and naming of the fast can vary between Śvetāmbara and Digambar communities, but the inner purpose remains the same: purify conduct and move toward spiritual progress. You can read more about upvas and its role in mokṣa here