In Jainism, there is no widely recognized festival named "Atham" (or Atham) in the standard Jain calendars. If you meant a different term (for example, a regional/colloquial name or a specific day like an Ashtami), please clarify the exact word or context.

Common Jain observances you might be thinking of include Mahavir Jayanti (birth of Lord Mahavira), Paryushan and Das Lakshan (forgiveness and purification), and the Samvatsari (the final day of Paryushan). If you can share the exact term or tradition you’re referencing, I can explain its Jain significance, how it should be observed, and how it fits within Digambar and Shwetambar practices.