Answer

In Jain Dharma, a 7-day fast is commonly called Atthai.

Explanation

Atthai means fasting continuously for 8 days in the common Jain usage, especially during Paryushan.

However, if someone fasts for exactly 7 days, it may simply be called a 7-day upvas or saat upvas.

Takeaway

A 7-day fast is usually referred to as saat upvas, while the well-known 8-day fast is called Atthai.