In Jainism, "Do Tithi" (also spelled "Do Tithi" or "Du Tithi") refers to a specific observance related to the Jain calendar. "Tithi" means "lunar day" in the traditional Hindu and Jain lunar calendars. "Do Tithi" literally means "two tithis," but in Jain practice, it specifically refers to the 2nd and the 7th days of each lunar fortnight (the Shukla Paksha and Krishna Paksha).

On these days, many Jains observe special practices, such as:

• Fasting (Upvaas): Some Jains perform fasting or partial fasting on Do Tithi.
• Restraint and Piety: Increased focus on spiritual activities, restraint (samayik), and study of scriptures.
• Remembrance: Do Tithi is considered auspicious and is observed in remembrance of the Tirthankaras and other significant events in Jain history.

The observance of Do Tithi is believed to help in reducing one's karmic bondage and progressing spiritually. The exact customs can vary among Jain communities and sects.

Summary: Do Tithi in Jainism refers to the 2nd and 7th days of each lunar fortnight, which are considered auspicious for fasting, spiritual activities, and self-restraint.