What does a misfiring on number 4 spark plugmean in obd 2 code?

That would be code P0304 which translates into cylinder #4 misfire. there are a few things that could cause this code. the sparkplug could be worn, there could be a mechanical issue such as a worn, bent or broken intake or exhaust valve in that cylinder or it could also be an engine management system problem such as a bad crankshaft sensor.