Shield

Your Shield is your first of three pools of points from which Damage will be subtracted. If your Shield reaches 0 and there is still Damage to be applied, the damage will then overflow into your Health. If that reaches 0 and there is still Damage to be applied, you will lose 1 Vitality, regardless of the amount of Damage remaining.
No Abilities will ever add to the points currently in your Shield Point Bank, but rather will always reset your Shield to a specific number. If your current Shield is higher than a new value, you can opt to keep the old value.