The Immaculate Conception is the Catholicdoctrine which says that Mary, the mother of Jesus, was conceived in the womb of her mother, Saint Anne, without original sin. The Catholic Church teaches this because they believe that Jesus, as God, had to be conceived in a mother whose soul was without any kind of sin, since God does not like sin. The Immaculate Conception became official Catholic teaching in 1854, announced by Pope Pius IX. Four years later, people claimed that Mary appeared to a girl named Bernadette in Lourdes, France, and that Mary told Bernadette: "I am the Immaculate Conception."
The Immaculate Conception does not mean the conception of Jesus in the womb of his mother Mary. This is correctly called the Incarnation.
The Feast of the Immaculate Conception is celebrated on December 8 each year.