Virginia had 13 legimate drives and scored 33 points. About 2.54 points per drive.
BYU had 12 legimate drives (end of game knee down series omitted) and scored 34 points (7 points on ST). About 2.83 points per drive.
BYU D vs Houston? 1.92 PPD.
BYU D vs Texas? 0.44 PPD.
BYU D vs UConn? 0.83 PPD.
The D's job is to stop the opposing offense from scoring each time they have the ball. Most games these days will see teams getting about 12 drive opportunities per game. BYU wants to limit its opponents to 23 points or less. Games where BYU's D is able to then keep its opponent's PPD to < 2, will allow them to reach this program pillar.
It is when teams, like Virginia, are over 2 PPD that we start to get into the danger of losing.