These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Durban King Shaka Intl Airport to Santa Ana J. Wayne/Orange Cnty Airport flight would often be abbreviated as a DUR to SNA flight. Los Angeles Airport (LAX), Ontario Airport (ONT), Burbank Bob Hope Airport (BUR), Long Beach Municipal Airport (LGB), Hawthorne Airport (HHR) are other airports near this flight route and their unique identifiers/IATA codes.