These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Newcastle Williamtown Airport to Rome Fiumicino Airport flight would often be abbreviated as a NTL to FCO flight. Venice Marco Polo Airport (VCE), Naples Airport (NAP), Catania Fontanarossa Airport (CTA), Milan Malpensa Airport (MXP), Bologna Guglielmo Marconi Airport (BLQ) are some additional IATA codes for airports related to your trip.