Vara
The weekday.
The seventh limb of the panchanga, and the only one that matches the civil week. Note that the Hindu vara runs sunrise to sunrise, not midnight to midnight — an event at 2 a.m. belongs to the previous vara.
What Vara governs
These vrats are defined by a weekday rather than a tithi, which is why they fall on the same day of the week and a different tithi each time.