In Jainism, the term Trivihaar Upvaas (त्रिविहार उपवास) refers to a specific type of fasting with certain restrictions related to the three types of activities (vihaar means "movement" or "activity"). The prefix "tri-" means three, and "vihaar" refers to activities. In the context of upvaas (fasting), Trivihaar Upvaas typically means observing a fast while abstaining from the following three activities:

1. Ratri-bhojan tyag: Avoiding food intake at night.
2. Anshan: Complete abstinence from eating and drinking, or sometimes only avoiding all food (water may be permitted in some traditions).
3. Ekantvas: Observing silence or staying in seclusion, limiting interactions.

However, most commonly in Jain fasting practice, Trivihaar Upvaas is described as a fast where one refrains from:

• Eating (आहार)
• Drinking (पेय)
• Rasa (रस; any kind of taste or flavor, including chewing things like betel leaf, supari, etc.)

This makes Trivihaar Upvaas a stricter form of fasting than ordinary upvaas, as it includes avoidance of both food and drink (sometimes even water).

Summary: Trivihaar Upvaas is a strict Jain fast where the aspirant abstains from all three: food, drinks (sometimes including water), and all kinds of taste. This is considered a higher austerity and is observed for spiritual purification, self-control, and accumulation of punya (spiritual merit).

Note: The exact interpretation and practice can vary among different Jain sects (Shwetambar, Digambar, etc.), so it is advisable to consult with a knowledgeable Jain monk or scholar for detailed observance in your tradition.