In Jainism, “Ashtami” (often spoken as “Aatham”) simply means the 8th tithi (lunar day) of each fortnight (both Shukla and Krishna paksha).

Its main significance for Jains is:

1. Day of special tapa (austerity)

- Many Jains keep upvas (fast), ekasana or aayambil specifically on: - Aatham (8th) - Chaudas (14th) - This is called pakkhi upvas – regular, planned fasting days every fortnight to reduce karma.

1. Favorable for pratikraman and samayik

- Because of the strong tradition of tapa on Aatham, people also do: - more samayik (meditation), - sutra‑paath, swadhyay (study), - pratikraman with more focus. - The idea is: on such days the mind is a little more detached, so spiritual practice gives deeper benefit.

1. Karmic and spiritual view

- Fasting and restraint on fixed tithis like Ashtami: - helps control raga‑dvesha (attachment & aversion), - supports ahimsa (less eating → less himsa in preparation of food), - becomes a regular ladder for progress even for grihasth (householders).

1. Digambar / Shvetambar

- Both traditions respect Ashtami as a good day for upvas and tapa. - Specific local customs (which tithi is stressed more, exact rules of food/water, etc.) may differ by sangh and guru, but the basic idea is the same: Ashtami = special day for self‑control, fasting, and bhakti.

You can read more about common Jain fasting days (including Aatham/Chaudas) here