"incoming damage sources are reduced by the amount of armor on this unit."
- Artifact Tooltip
Armor is a stat used by Heroes and Creeps alike. It reduces incoming damage by a set amount.
Interaction with damage
Normal damage is reduced by armor. For each point of armor, the final damage of an attack will be lowered by one.
Piercing damage completely ignores armor. Negative armor still makes you take more damage.
Siege damage is not hindered in any way by the armor on a blocking unit, but will deal less damage to the tower if the tower itself has armor.
Artifact 2.0 Beta
"Now each point of armor can block one point of damage and is refreshed at the beginning of the round."
Negative armor will cause the affected unit to take more damage than the attack would have done otherwise.