Polarized hull plating
Polarized hull plating is a defensive technology used on Earth starships in the 22nd century. Supposedly an electromagnetic field of some sort reinforces the ship's hull, helping it resist damage. For all practical purposes, it serves as a low-performance defensive shield, although it actually seems to function more like a structural integrity field.
Because the show treats it the same as shields, we end up with the dubious situation of being able restore downed sections of the ship's hull plating by applying extra power to the system. For a better breakdown of why this is stupid, watch Chuck's review of the Enterprise pilot.