Here we go. Wikipedia to the rescue:
"The virginal conception of Jesus by Mary is at times confused with the Roman Catholic Church teaching of her "Immaculate Conception", namely Mary's conception by her mother and father in the normal way, but free from original sin. While the Virgin birth of Jesus relates to the nativity of Jesus, the Immaculate Conception relates to the nativity of Mary. The Roman Catholic doctrine of Mary's Immaculate Conception has been defined as follows: "The most Blessed Virgin Mary was, from the first moment of her conception, by a singular grace and privilege of almighty God and by virtue of the merits of Jesus Christ, Saviour of the human race, preserved immune from all stain of original sin.""