Jaya Ekadashi and Vijaya Ekadashi
Ekadashi is the eleventh day of a fortnight in a Hindu lunar calendar and is dedicated to Lord Vishnu.

There are two Ekadashis in a lunar month. The two Ekadashi in the month of Maha are known as Jaya Ekadashi and Vijaya Ekadashi Upvaas or fasting on Ekadasi day is considered highly beneficial and is observed by a large number of Vishnu devotees.

Significance:
Extract from the sacred Skanda Puran:-

Lord Sri Krishna said, “I shall tell you about Jaya Ekadashi. This Ekadashi obliterates all kinds of sinful reactions and demoniac influences that may be affecting the spirit soul. It is known as Jaya Ekadashi, and the fortunate soul who observes a fast on this sacred day is relieved of the great burden of ghostly existence.

Thus there is no better Ekadashi than this, for it truly bestows freedom from birth and death. It is to be honored very carefully and diligently. Therefore one should strictly observe a fast on the sacred day of Lord Hari, especially on this Jaya Ekadashi. A great soul who observes this fast with full faith and devotion has in effect given all kinds of charity, performed all kinds of sacrifice, and bathed in all the Holy places of pilgrimage.

Fasting on Jaya Ekadashi qualifies one to reside in Vaikuntha and enjoy unending happiness for billions of yugas – indeed, forever, as the soul is eternal. One who even hears or reads these wonderful glories of Jaya Ekadashi achieves the blessed merit attained by performing an Agni fire sacrifice – Havan, during which the hymns from the Sama-veda are recited.”

Whoever observes it certainly achieves success in this life and the next.