An innate “defensive” stat that enemy monsters possess. Each of your cards’ individual damage is reduced by the enemy’s defense prior to dealing any damage to enemy HP; if defense is greater than damage dealt by a card, that damage is reduced to one. For example, if each of your cards do 1,000 damage to an enemy with 900 defense, you will deal 600 total damage; each attack is reduced from 1,000 damage to 100 damage by the enemy defense, and then six attacks altogether deal 600 total damage.
Ways To Bypass Defense
True Damage is a specific characteristic of attacks which deal damage that ignores enemy defense. Leader skills (such as that of Dark Dracoblader of Scattering Clouds, Ina
), active skills (such as that of Phantom Demon of the Grimoire, Ilmina
), and awakenings (such as 
Super Bonus Attack) can all output True Damage.
A monster with the 
Guard Break awakening will have its own damage ignore all enemy defense values if all attributes are present on the team and matched on the board.
If a monster does not have a 
status immunity shield, monsters with certain active skills such as Shiva
can reduce or nullify its defense.