The Immaculate Conception is a belief in the Catholic church, as well as some Protestant denominations, that Mary, the mother of Jesus, was protected by God from the original sin during her own conception. Since she subsequently lived a life completely free from sin, this makes her perfectly pure. The idea of the Immaculate Conception is often confused with the doctrine of the Incarnation and Virgin Birth of Christ.
The Immaculate Conception was defined as dogma by Pope Pius IX in 1854
and consecrated by Pope Pius XII in 1942. However, this tradition had existed
within the Catholic church for more than a millenium. Eastern Orthodox
Christians do not believe in the Immaculate Conception, because they have
a different view of the original sin from Catholics, and in their tradition,
it would be unnecessary for Mary to require divine purification from this.
The majority of Protestants reject the idea because it is not explicitly
stated in the Bible.
See: El Greco The Immaculate Conception.
Bartolomé Esteban Murillo Our Lady of the Immaculate Conception.
Francisco de Zurbarán Our Lady of Immaculate Conception, The Immaculate Conception.