Here is the simple, traditional Jain meaning (used especially during Paryushan):

• Chauvihar: After sunset, take nothing at all—no food and no water—until the next sunrise. This is for ahimsa (night‑born beings) and for saiyam (self‑control).

• Tivihar: After sunset, do not take any food; only water is permitted. Traditionally, the water should be properly filtered (and many observe boiled water). Some communities keep an extra caution of taking water only in daylight.

During Paryushan

• Both are observed more strictly: finish your last bite and last sip before local sunset; resume after sunrise.
• Take pachchakkhan (a vow) for what you will observe that night/day.

Notes by tradition

• Shvetambar: In Chauvihar, no water after sunset. In Tivihar, water is allowed; many keep it boiled/filtered and often limit it to daylight as an extra caution.
• Digambar: No eating after sunset is the norm. On stricter vrats and for sadhus, water is also avoided after sunset; for laypeople, Tivihar allowing water exists but many still prefer no water after sunset in practice.

Essence

• Chauvihar = after sunset, nothing at all.
• Tivihar = after sunset, only water allowed; no food.

For quick clarifications and examples: