Tritiya is the third tithi of the bright fortnight, when the waxing crescent has grown clearly visible in the western evening sky. It falls in the Jaya group of the fivefold classification, the days associated with victory and gain, and its presiding deity is traditionally the goddess Gauri, a form of Parvati. Several observances attach to it: Akshaya Tritiya, in the bright fortnight of the spring month of Vaishakha, is regarded as one of the most auspicious days of the whole year for beginnings, purchases, and charity, its name meaning the imperishable third. In the panchanga the day is read as favourable and prosperous. These are the conventions of the calendar tradition, laid over the simple astronomical fact of the Moon drawing steadily away from the Sun.
Akshaya Tritiya's name, the imperishable third, reflects a belief that merit earned or gifts given on this tithi does not diminish, a reasoning distinct from the ordinary Purna, Nanda, Bhadra, Jaya and Rikta fivefold classification that grades every tithi's general character; a day can be Jaya by the standard grouping and still be singled out by name for an entirely separate reason tied to a particular festival tradition. Like every tithi, the third's real duration varies with the Moon's changing speed, and the day is one of the small number of tithis in the Hindu calendar, alongside Vijayadashami and the first day of a lunar month in some regional practices, that some almanac traditions treat as swayam siddha, self-auspicious, meaning it does not require an additional check of nakshatra or other panchanga limbs before undertaking major life events such as marriage.