If you mean Updhān / Upadhān Tap in Jainism, it is a special and strict austerity (tap) observed by śrāvaks/śrāviks for spiritual purification. It is usually done under guidance and includes fasting, ekāsan, paushadh, japa of Navkar Mantra, pratikraman, study of scriptures, and disciplined conduct. ( jainworld.jainworld.com)

Traditionally, it is performed in structured durations such as 47 days, 35 days, or 28 days, with different internal stages in the longer forms. Its main purpose is to reduce karmic bondage, increase self-discipline, and deepen devotion. ( jainworld.jainworld.com)

If you want, I can also explain its vidhi and meaning in simple Gujarati/Hindi/Jain terms.