Tithi

The lunar day — one of the five limbs of the Hindu Panchang.

A Tithi is a lunar day — the time it takes for the Moon to advance 12° from the Sun. There are 30 tithis in each lunar month, 15 in the waxing phase (Shukla Paksha) and 15 in the waning phase (Krishna Paksha). Tithis are fundamental to Hindu festival timing, vrat observances, and the auspiciousness of any undertaking.