Damage resistance varies with a Ship's class and changes the amount of damage a ship receives from a given source.
For example, suppose a Battlecruiser had 2500 Shield and it was hit by a Turret with a base damage of 125. The true damage the ship would take would be reduced by the percent relative to the ship's class, in this case, Battlecruiser. If Battlecruisers had a base damage resistance of 0-5%, the ship would take a maximum of 125 damage (0% reduction) or a minimum of 118.75 (5% reduction; 125 - 5% of 125 = 118.75).
Damage resistance values were updated in version .70. Most ships saw increases in resistance. Miner/Freighter resistance was increased from 10 to 15%; Frigate resistance was increased from 20% to 25%; Dreadnought resistance was increased from 35% to 38%; Super Capital resistance was increased from 35% to 42%; Alien resistance was decreased from 30% to 25%. Additionally, Starbase resistance was decreased from 50% to 45%.
It was further altered in .71c.