Hymenal Bleeding (Dam Betulim)
With first intercourse, the hymen (a membrane that partially covers the vaginal opening) is stretched and may tear slightly, leading to bleeding. This bleeding is called dam betulim (blood of virginity). Dam betulim renders a woman niddah by rabbinic enactment.
The laws of dam betulim apply to a virgin bride after first intercourse, whether or not she actually bled.
This section addresses the halachot of dam betulim.