Hull

Hull is the second main line of defense for your ship. If this fails on one section you'll be dead in seconds if you keep getting hit there, but also note that even while you still have Hull damage to it can partially penetrate through to your equipment, weapons, etc, damaging or even disabling it. If your Shields and Hull on one side are both about to fail make sure to turn your ship so that side of it isn't exposed to the enemy, or you won't last long.