The term "immaculate conception" is often used generally to denote the
conception of a child by a woman who has not engaged in sexual intercourse, and specifically to the conception of Jesus by the Virgin Mary. Both usages are incorrect.
"Immaculate Conception" refers to neither the conception of Jesus nor to a virgin birth. It is a specific doctrine of Roman Catholicism decreeing that the Virgin Mary was preserved free from original sin by divine grace from the moment of her conception. Although this dogma had been argued since the twelfth century, it was not made official until 1854 by Pope Pius IX. Since then December 8 has been observed as a Roman Catholic feast in commemoration of the Immaculate Conception.
|Immaculate Conception (Catholic Encyclopedia)