If you mean nine consecutive days of complete Upvas (fasting), it is commonly called “Navai” or “Nav Upvas” in many Jain sanghs. Unlike 8 days (Atthai) or 10 days (Dasai), nine-day Upvas does not have a single classical name used everywhere, so Navai/Nav Upvas is a practical/regional term.

If you mean the well-known nine‑day Tap observed twice a year, that is Ayambil Oli, also called Navpad Oli. This is nine days of Ayambil (one very simple, tasteless meal each day) with worship of the Navapad.

• Shwetambar: emphasizes Siddhachakra/Navpad Oli with daily Ayambil and puja.
• Digambar: observes Navapad Aradhana; the spirit of nine days’ tapasya is the same.

For a simple explanation of Navpad/Ayambil Oli, see: and