In Jainism, an eight days fasting is known as Ashtanhika Tap or Ashtanika Parva. However, the most well-known extended fasting practice is Paryushana, during which many Jains observe fasts of varying lengths, including up to eight days or even longer.

Eight days fasting (Ashtanhika Upvas) involves abstaining from food (and sometimes water) for eight consecutive days. This practice is considered a very advanced and rigorous form of tapasya (austerity), undertaken for self-purification, spiritual upliftment, and to accumulate spiritual merit (punya).

Key Points about Eight Days Fasting in Jainism:

• Purpose: It is performed to purify the soul, reduce karma, and practice self-control (samyama).
• How It Is Observed: The devotee refrains from eating any food, and in more advanced forms, may even abstain from water (nirjal upvas).
• When Is It Done: While Paryushana is the most common period for such fasts, some may also observe it during other auspicious Jain festivals or personal vows (vratas).
• Spiritual Significance: Such fasting is believed to help destroy past karmas, cultivate detachment, and strengthen one's resolve on the path of liberation (moksha).
• Support and Guidance: It is generally undertaken with guidance from learned Jain monks or nuns, and devotees are often encouraged to listen to spiritual discourses and engage in meditation and prayer during the fast.

Note:

Fasting is a voluntary spiritual discipline in Jainism and is not compulsory. It should always be undertaken considering one's health and capacity, and in the spirit of devotion and spiritual progress, rather than merely as a ritual.

In summary: Eight days fasting in Jainism is a significant spiritual practice aimed at self-purification and accumulating merit, primarily observed during festivals like Paryushana or as part of personal penance.