Denver Broncos drove the ball basically to Carolina's goal line, and was about to score, when the Panthers stopped them on 3rd down, leading to 4th down mean basically the Broncos would be forced to kick a field goal, and Carolina gets the ball back with a couple minutes left. But wait - a flag for defensive holding against Carolina. So instead of the Broncos having to kick the ball on 4th down, the Broncos now have the ball still, half the distance to the goal, 1st down again.
It was essentially the absolute last little shred of hope for the Panthers to mount a miracle come back, destroyed, and the end of Cam Newton's season and Superbowl dreams.