The Assumption of the Virgin Mary is celebrated on the 15th of August and celebrates the resurrection of Mary, Mother of Jesus.
Without sin and mother of the only Son of God, she was the first after Christ to be resurrected.
The Assumption bodes the resurrection of the flesh that will take place after the Last Judgement for all of humanity. It is a Catholic feast; Orthodox churches celebrate the feast of the Dormition of the Mother of God on the same day.