“Pochisom” is not a standard Jain term I can identify from authentic Jain texts or common Jain practice. It may be a misspelling or a local way of saying one of these:

• Pakshi/Chaudas (Pratikraman days): Fortnightly Pratikraman done on the 14th/15th lunar day; sometimes people mention the weekday with it (e.g., done on a Monday). See a simple Pratikraman overview here:
• Proshadh (Poshad) Upavās: A fast observed on the 8th and 14th lunar days, focused on restraint and scriptural reflection. Basic fasting types are also covered under Pratikraman/Avashyaks resources:
• “Pachchisi” (25): In some explanations, lists of 25 faults/categories appear in Pratikraman teaching; this is unrelated to a weekday name but sometimes the number “25” (pachchīs) gets mixed into speech.

If you can share the exact spelling or the context (festival, fast, or a sutra name), I can give the precise Jain meaning and usage accordingly.