Defense represents the components used by ships and starbases to protect against weapons. There are three main types of defensive capabilities.
Each type of defense is strongest against a particular class of weapons. Armor is strong against mass drivers. Shields are strong against Lasers. Point defense is strong against missiles. Defense operates at the full rated strength when defending against the weapons they are designed to defend. Defense operates at the square root of strength against weapons of other classes. This property encourages civilizations to develop weapons that their enemies do not have defenses for, and defenses against the weapons that their enemies typically employ.
Defense can be improved on all ships by a percentage due to Race bonus, Mining starbases, or specific Technologies. These bonuses will show as increased defense levels compared to components on ships. For example, a 20% Defense bonus will give a ship with 5 Shields effectively 6 in combat.