You'll never know unless you ask (or search )
Decat? Is where you replace your cat (catalitic converter) with a straight-through pipe, replacing the cats completely. This won't pass an MOT
Cat back? The exhaust section from the catalitic converter backwards (not including cats) so mid section and back box.
Bungs? I don't know! Probably baffles that go in the back box, sometimes removable.
Race cats. AKA high flow cats. Allow more airflow through the cats and usually louder. Most will pass an MOT, although techincally I think they're supposed to be marked with a british standard, though doubt many, if any, would check.
Hope that helps a little...
Bungs are fitted in the tail pipe to reduce noise
Lambda sensors are in the cats & not the exhaust, all hiflow/de cats for the Z have bungs to refit the sensors.
MOT with decats = fail
Everything else "should" pass