In Jainism, upvas (also spelled upvaas or upavasa) refers to fasting, usually by abstaining from all food (and sometimes water) for a specific period, typically from sunrise to sunrise. Fasting is an important austerity (tapa) and spiritual practice to purify the soul, reduce karmic bondage, and cultivate self-control.

12 Upvas (Baaras Upvas)

• Performing 12 upvas refers to observing a fast on any 12 days, not necessarily consecutively, within a fixed period (often a month or a year).
• Some Jain communities believe that performing 12 upvas with proper discipline, devotion, and intent brings significant spiritual merit and is considered a basic or introductory goal for laypersons.

13 Upvas (Terah Upvas)

• 13 upvas refers to fasting for 13 days, often consecutively, which is a more rigorous and advanced austerity.
• Completing 13 upvas is considered a greater spiritual achievement and is sometimes associated with special vows (vratas) or penance performed for spiritual upliftment or atonement.
• 13 upvas is often seen as an extension or progression beyond the 12 upvas, symbolizing greater self-control and renunciation.

Significance

• Both 12 and 13 upvas are respected practices in Jainism, but 13 upvas is regarded as a higher level of austerity.
• The exact significance and practice can vary depending on the Jain sect (Shwetambar or Digambar) and local traditions.

In summary:

• 12 upvas: Basic or regular spiritual practice, done on 12 days.
• 13 upvas: More advanced, often consecutive, shows deeper renunciation.

Both are means for laypersons to accumulate spiritual merit (punya), destroy karma, and progress on the path of liberation (moksha).