Paryushana (or Paryusan) is one of the two most important festivals for the Jains, the other being Diwali. Normally Svetambara Jains refer it as Paryushana, while Digambara Jains refer it as Daslakshana. Paryushan means, literally, "abiding" or "coming together". It is also a time when the laity take on vows of study and fasting with a spiritual intensity similar to temporary monasticism.[1][2] The duration of Paryusana is for 8 or 10 days and comes at the time when the wandering monks take up temporary residence for four months of monsoon. In popular terminology, this stay is termed chaturmasa because the rainy season is regarded to be about four months. For this minimum duration, Paryushana must be initiated by Panchami (fifth day) of the Shukla Paksha phase of the Bhadrapada month. In the scriptures it is described that Lord Mahavira used to start Paryushana on Bhadrapada pak sha panchami. After Mahavir, nearly 150 years Jain Samvatsari was shifted to Chaturthi (4th day of Bhadrapada of Shukla phase. Since 2200 years Jains follows Chaturthi.
The date for the Paryushana festival is thus Bhadrapada Shukla Chaturthi for both major sects. Because of computational and other differences, there can be some minor differences among various subsects. Recently there has been an attempt to standardize the date. Because at this time the monks have settled in the town for a longer duration, it is time for the householders to have an annual renewal of the faith by listening to the statement of the Dharma and by meditation and vratas (self-control). In the Digambaras, it is done by starting a 10-day period from Paryushana (Bhadrapada Shukla panchami) during which the dashalakshana vrata is undertaken. In the Shvetambaras an 8-day festival is celebrated that ends with Bhadrapada Shukla chaturthi. The last day is called Samvatsari, short for Samvatsari Pratikramana.
(... from Wikipedia on 2012-04-18 00:13:42)