“20 Sthanak” usually means 20 Sthanak Tap (वीस स्थानक तप).

In simple words:

• It is a very big Jain tap (austerity).
• A person does 20 “sthanak”, and

each one sthanak = 20 upvas (fasts) done with proper rules and bhav.

• So total = 20 × 20 = 400 upvas in the whole vrat.
• These fasts are done under guidance of a Guru / Acharya, with:

- strong samyak darshan (right faith) - compassion for all jivas - and desire for moksha, not for worldly name–fame.

In Jain tradition it is believed that all Tirthankars performed this tap in their 3rd last birth, so it is considered a Tirthankar-bhavi tap (austerity suitable for a future Tirthankar).

Details (exact pattern of fasts, rules, time gap between sthanak, etc.) can differ a little between sanghs and traditions (Śvetāmbara / Digambara), so for actual practice one must take pachchakhān and full guidance only from one’s own Acharya / Guru.

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