It's the vacation you take shortly before the baby arrives. The wife and I took one (though I refuse to call it that). For the record, we probably spent about $250 on the whole trip (including fuel, lodging, food, etc).
We took one as well, but didn't know it had a name.
I got a last minute deal and it cost a few hundred bucks as well.
Before or after conception? We took one before and just called it a "honeymoon."
No about 8 weeks before delivery. The last time such a thing could be done for a long, long time.