Board Thread:Game Discussion/@comment-11179649-20131009160312/@comment-23.30.137.141-20131009163308

I believe it's health points. But the P is irrelevant. Basically, your card can take on so much damage, it's total HP. Defense helps reduce the damage taken, but the attack subtracts from the cards HP. Once your card has 0 HP, it's removed from the battle.