In Jainism, "Tivihaar Upvaas" (also spelled Tivihar Upvas) refers to a specific type of fasting (upvaas). "Tivihaar" means abstaining from three types of "vihar" (intakes):

1. Ras (taste, or intake of food)
2. Paan (drinking)
3. Naach (chewing, or consuming anything by mouth)

So, during Tivihaar Upvaas, one refrains from:

• Eating any food
• Drinking any liquids (including water)
• Chewing anything (even mouth fresheners, etc.)

In essence, Tivihaar Upvaas is a very strict form of fasting where nothing is consumed by mouth for the entire fasting period, not even water. This is considered a higher form of austerity and self-discipline in Jain practice, and is observed by some laypersons and ascetics, especially on important religious days.

This fast is different from other types such as Ekaasanu (one meal a day) or Biyaasanu (two meals a day), and even stricter than Chauvihar Upvaas (where nothing is consumed after sunset up to the next sunrise, including water).

Summary: Tivihaar Upvaas in Jainism means a complete fast where nothing is consumed by mouth—no food, no water, nothing at all—for the duration of the fast.