Characters may have or gain abilities that provide them protection (aka armour).
AA is a numerical damage reduction (e.g if a blow does 3 points of damage, and you have 1 point of armour - you take only 2 damage).
AA can never reduce damage taken below one point.
Through damage ignores AA
A Characters Armour Allowance may be depicted in any way that you wish so long as there is some rational reason behind it. It may be that you are wearing clothes made from spidersilk, the fabric has been encrusted with shells from deep ocean crabs. It may be that the sight of you running around in nothing but a loinskin puts off your opponents. The reason is up to you.