What does "Armor -0" mean?

Sometimes when my ships are taking down an enemy’s shields, I’ll see hits for “Armor -0” among the “Shield -X” messages. Why is it giving me this message?

At first I thought it was “Armor -8”, but I’m positive it’s a zero not an eight.

Cameron

It means that the damage “pierced” the shield and hit the armor, however, not enough got through the shield to deal any damage to the armor.
And yes, the shield did take damage.

edit: All hail the mighty edit button!

To be a bit more technical, what’s happening is that one of your opponent’s shields has gone down, and since incoming damage is spread equally among every shield module some of that damage is hitting a shield module that isn’t up and therefore going through to the armor. It’s not piercing, per se, and there’s not ‘leftover’ damage that isn’t strong enough to crack the armor; it’s just that the weapons you have which are randomly hitting the armor don’t have enough armor penetration to get through the target’s armor strength.