Natural armor bonus

The Natural armor represents a creature's hide or magical effects that make skin thicker (such as Barkskin). Natural armor provides a bonus to AC. Natural armor bonuses do not stack with each other.

Sources of Natural Armor:
 * Item: Pre-Order Amulet +1
 * Item: Hammer of Life (Dragon Loot) +2
 * Spell/Potion: Barkskin +2-5
 * Crafting Property: *Dragontouched Armor Sovereign Rune +4.

Other common bonuses to your armor class are armor bonus, shield bonus, deflection bonus, dodge bonus, dexterity bonus, and miscellaneous bonus.