Immaculate Conception: usual reference is in relationship to the birth of Jesus who had no earthly father who impregnated Mother Mary, but rather was a result of the Holy Spirit's impregnation. Edgar Cayce's channelings of the Universal Mind state that Mother Mary was born of the immaculate conception as well! Impregnation by the Spirit of God
The belief that before the birth of Mary (the mother of Jesus) was born, she was preserved from original sin at the time of her conception, circa 20 BCE. It is widely but incorrectly believed to refer to Jesus' conception, circa 5 to 8 BCE.
Roman Catholic holy day first celebrated in 1854