Number of shields determines how resilient to enemy attacks your character currently is.
After playing a card your characters defense is set to the number of shields printed on a card plus extra ones from special abilities. The defense rating i lowering the enemy's attack value, however is not protecting from deplete nor banish effects.
In game descriptionEdit
You've drawned a card with shielding! Each point of shielding you have will reduce the amout of damage you take on your opponent's turn by one. Shields revert to 0 at the beginning of your turn.