Armor is a character stat that represents resistance to physical damage. For each point of armor, the amount of incoming physical damage a character receives is reduced by one. In battle, a character's armor is indicated by the number of blue shields on that character's hero portrait.
Walling with an allied character grants both characters an additional point of armor, though each character can only benefit from this bonus once.
Armor can be acquired from multiple sources, including a character's gear, their class, and various events. Non-integer armor values are always rounded down to the nearest whole number for combat purposes.