This festival celebrates the birth of Vamanji, the fifth incarnation of Lord Vishnu, on Bhadarva sud 12, the day after Parivartini Ekadashi.

Origin :
The shastras cite that Prahlad's grandson, King Bali performed a grand Ashwamegh Yagna at Bhrugukutch (Bharuch) on the banks of the river Narmada. Of the 100 yagnas to be completed, he was performing the final. And one who performed 100 yagnas became Lord Indra. The threat of being toppled frightened the reigning Indra, who divulged his predicament to Aditi, his mother. He also informed her of the three insuperable weapons, already procured by Bali from a previous yagna: a divine chariot, a wishing plate and an indestructible armour. With these he could reign terror and attain victory. In turn, Aditi informed her consort, Kashyap, of their son's imminent doom.
Kashyap advised her, "Accept the Lord's refuge and offer sincere devotion. Devotion offered by the meek bears fruit more easily than by anybody else."
Aditi therefore performed a twelve-day vrat known as Payovrat. This pleased the Lord, who granted her a boon to resolve her problem.
As a result Lord Vishnu was born to her as Vamanji - a dwarf - on Bhadarva sud 12. In the garb of a brahmachari, he approached King Bali at Bhrugukutch.
The Shatapatha Brahmana cites a slightly different version. When the devas battled with the demons, the latter won. They then began to divide the Earth among themselves. Lord Vishnu arrived as Vaman and demanded some land for the devas. The demons agreed to grant only three strides of land. At that instant Vaman turned into a gigantic form and swiped all the three worlds.
King Bali welcomed the brahmachari. He requested him to ask for whatever alms he wished.
Vamanji replied, "O King of demons! I only wish for a three strides of land."
Astonished, Bali said, "O Batuk, you are just a little boy and do not understand things. What can you do with three strides of land? At least ask for enough land to will sustain you."
The Lord chuckled. "O king! He is happy who accepts that which is granted by the Lord. Such contentment is the root of moksha. Conversely, one who has not subdued his senses will not be content with even the three worlds."
This pleased Bali, who pledged to grant some land. When Shukracharya, the guru of the demons heard of his pledge, he arrived hotfoot. He warned the king, "O Bali! He is none other than Lord Vishnu. He'll take everything." But King Bali remained undaunted, keeping his word. Shukracharya cursed him. Bali accepted the curse.
At that instant, the little Lord transformed into a colossus. In one stride he covered the whole of earth. With his second he covered the sky and heavens, including Maharlok, Janlok, Taplok and Satyalok! "Where should I now place the third stride?" he asked Bali. With humility, Bali replied, "O Lord, set your foot (third stride) on my head." Vamanji then placed his foot on Bali's head and drove him down into Patal. Pleased with the demon king's selfless devotion, the Lord granted him a boon to remain at his doorstep. King Bali's wife, Vindhyavali, wholeheartedly supported his gift to Vamanji.
It is reported that Vamanji's ashram is situated in a town named Baksaar in the Shahaabad district of Bihar. On this same site, the rishi Vishwamitra founded his own ashram. The Vaman Puran cites 131sacred places of Lord Vamanji.

Ritual :
Devotees observe a "faraari" fast for half a day, taking normal food from the afternoon.