From the 19-KopongKopong phrase, do you know what is kopongkopong?

Tweet

I've just learned that in the phrase "Panahon pa ni Mahoma", that Mahoma is the Spanish translation of Mohammed, the great teacher of Islam, so it means that the one referred to in the phrase is very old since it is since Mohammed's time. I'm now curious about the phrase 19-kopongkopong, does anyone know where it comes from?