Vrata is a vow.
Vows are depending on the day of the week, the season, the position of the planets, fasting, pilgrimages, donations, keeping silent (mauna). They are always combined with a wish.
The Vrata is followed by the Utsava, the celebration of joy as a reward for effort.
Every Vrata has its story (Katha), the narrations are called Vrata Katha.
Find a collection of Vrata Katha here