Defense is the character stat which reduces damage taken from physical weapons. A higher amount of Strength is needed to overcome a high Defense. Knights and Generals are known to have high Defense, whereas classes such as Mages, Sages and Monks usually have lower defense. A Dracoshield is an item available in most Fire Emblem games that permanently raises a character's defense stat.
When a unit is hit with a physical weapon, each point of the victim's defense reduces the attack's damage by one point. In most games in the series, the damage can be reduced all the way to zero in this way, but such no-damage attacks can still Poison targets if the weapon can inflict poison.
Defense has no effect on magical attacks (which are normally reduced by the Resistance stat), or damage received from lava tiles (which is always 10 regardless of defense or resistance). Also, some Skills, such as the Luna and Pierce, gives attackers a chance to bypass the victim's defense.