Ayambil 81 days is about Navapad Oli (Navpad Oli), a specific rhythm of Ayambil vows observed by many Jains.

• What it is: Ayambil is a vow of eating only one simple, tasteless meal a day (often boiled, without oil, ghee, milk, sugar, salt, or spices) and keeping strict restraint in food. Navapad Oli is the practice of doing Ayambil for 9 days twice a year, i.e., 9 days in the bright half of Chaitra and 9 days in the bright half of Ashwin. When you count both halves over the years, it adds up to 81 days of Ayambil in total, spread across multiple cycles. This extended sequence is called Navpad Oli because it centers on the nine Navpad (the nine supreme spiritual aspects/entities) during the practice. ( jainpedia.org)

• The number 81: Observing 9 days × 2 (per year) repeatedly for several years adds up to 81 days. This is why you’ll sometimes hear that Navpad Oli can be completed in 4½ years, totaling 81 days of Ayambil. The practice also emphasizes worship, meditation, and reflection on the Navpad (the nine noble aims) during the days of the vow. ( jainpedia.org)

• Doctrinal notes:

- It is widely observed by both Digambar and Shwetambar traditions, though local practices and emphasis can vary. - The core idea is purification of karma through steady, disciplined restraint and devotional practices during the Ayambil days. ( yja.org)

• Practical gist for a beginner:

- Eat only one plain meal each day during the Ayambil days. - The meal should be simple and free from taste-enhancers (no milk, ghee, sugar, oil, etc., as per common guidelines). - There is often accompanying Navpad Aradhana (worship of the Navpad) and devotional practices during these days.

If you’d like, I can point you to a Jain Knowledge resource that explains Navpad Oli in more detail.