As we know, the Immaculate Conception refers to the conception of Mary, Jesus’ mother.
The birth of Jesus is known as the Virgin Birth.
So we’ve got terms of art for Mary’s conception and Jesus’ birth. I’ve never heard one for Jesus’ conception that I can recall.
There’s the Annunciation, but that’s Mary being told that she would conceive Jesus. Close, but no cigar.
A bit of Googling turns up the term ‘virgin conception’ for Jesus’ conception. But it isn’t clear just how generally accepted it is, or whether any major church or religious organization uses it. (And since I’ve never heard it before, I’d expect blank looks or their equivalent if I ever used it in conversation, or on a message board or in blog comments or wherever.)
Just as a data point, the Spanish name “Encarnación” (as in MLB player Edwin) is in fact a reference to the Incarnation. That is the term I learned in my early church school days.
My Googling says that the Incarnation is celebrated by Christians at Christmas, so the connection between the Incarnation as a theological concept and the event of Jesus’ conception specifically seems a bit fuzzy at best.
But technically, that wouldn’t be accurate either (though close).
The OP asked about ‘conception’, which is when the sperm combines with the egg. This takes place something like 45 minutes (minimum) to 12 hours after ejaculation. So that’s still not a completely accurate term.
March 25th is the Feast of the Annunciation. As in “I announce to you that you’re gonna have a baby” “uh… you know, I didn’t study biology but I’m reasonably sure that’s not how it works” “girl, God says you gonna have a baby” “ok then but I still think this is kind of weird!” The feast is set on that day by the method of “ok, nine months before the birth, March 25”. We just don’t have separate names for the conception, the implantation, the Holy Placenta…
The Incarnation mostly gets attention around Christmastime, because that’s when we’re doing the Origin Story of Jesus, so to speak. It doesn’t mean that it actually happened at Christmas. Heck, Christmas probably didn’t happen at Christmas, either. Doesn’t matter.
