Super Capital Ship is a class of heavy starship including Carriers, Cruisers, Battlecruisers, Dreadnaughts and prior to the Homeworld 2 Era, Destroyers.
There are not many units that can compete with Super Capital Ships with tonnage, and they are unbeaten with firepower. While requiring vast amounts of manpower, resources, and sophisticated technology to be built, these units can serve as a fleets core.
Most Super Capital Ships can destroy any Capital Ship in matter of seconds. However almost all Super Capital Ships share the same weakness: a lack of effective anti-strike craft defense. Most of them have few point defense guns, while some of them don't have any weapons that could be a threat to bombers. Therefore a Super Capital alone can be destroyed by squadrons of bombers without significant losses. However it's very uncommon to find Super Capital Ships alone, as their construction cost is so high that they are rarely an acceptable loss in battle.
Improvements made during the Homeworld 2 Era allowed this class of ship to build its own subsystems making them more flexible and even useful.