These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Penang Intl Airport to San José Juan Santamaria Intl Airport flight would often be abbreviated as a PEN to SJO flight. Liberia Airport (LIR), Limon Airport (LIO), San José Tobias Bolanos Intl Airport (SYQ), Tamarindo Airport (TNO), Quepos Airport (XQP) are other airports near this flight route and their unique identifiers/IATA codes. Find deals