In Jainism, Choviyaar Upvaas refers to a specific type of fasting and food observance:

• Upvaas means fasting, where a person abstains from all kinds of food and sometimes even water for a set period, usually from sunrise to sunrise (approximately 36 hours).
• Choviyaar (also spelled "Chovihar") is the practice of not eating or drinking anything after sunset (generally after the time when there is still enough light to see the lines on your palm). This is a daily observance for many Jains, aimed at minimizing harm to living beings that are more active or come out after dark.

So, Choviyaar Upvaas is a fast where, in addition to the regular fasting rules, one particularly observes the discipline of not consuming anything after sunset (Choviyaar). This combination is considered a stricter and more meritorious form of fasting in Jainism, as it involves greater self-control and ahimsa (non-violence).

In summary: Choviyaar Upvaas = Fasting (Upvaas) + Strictly no food or water after sunset (Choviyaar)