I was dong a Bible study in prophecy and it mentioned the New Moon. And I looked in my bible dictionary. And I found it was the time when you see no moon in the sky. I used to think the New Moon was the full moon. But I do not watch the evening sky like I used to !

---editorial comment-------
The Biblical new moon is what's known now as the crescent new moon. It's defined as the time when the first sliver of the crescent moon appears, not the dark nights of the moon's cycle. It's not obvious because the term has changed meaning over time. The astrological new moon is the totally dark moon. The crescent new moon is the moon used by God to mark the beginning of a month.