This is just an IATA (International Air Transport Association) code. IATA codes are used in aviation to identify and differentiate airports. That’s why a Taipei City Taiwan Taoyuan Intl Airport flight would often be abbreviated as a TPE flight. Taipei City Sung Shan Airport (TSA), Taichung City ChingChuanKang Airport (RMQ), Hualien City Airport (HUN) are other airports near this flight destination and their unique identifiers/IATA codes.