The hair on the back of ones neck. Usually connects to back hair. It is unknown as to whether or not the neckbeard is formed from the hair on the back or from the hair on the head. Neckbeards are easily controlled with regular and proper maintenance.
"Man, does that guy ever have a massive neckbeard!"
"I thought that it was a tattoo, but it turned out to be just a neckbeard."
Wes groomed his neckbeard before his big date.