There are 3 main types of Āyambil (based on duration and vow):

1. Single Āyambil – doing the fast for one day.
2. Āyambil Olī (Navapad Olī) – 9 consecutive days of Āyambil.
3. Navpad Olī series – nine such 9‑day Olīs done over the designated years (total 81 days of Āyambil).

All three follow the same basic rule of Āyambil (one time, bland meal without vigai), they only differ in how long the vrata is continued.

You can read a simple explanation of Ayambil Olī here