USM meaning in Airport Code ?

Ko Samui (or Koh Samui, also often locally shortened to Samui; Thai: เกาะสมุย, pronounced [kɔ̀ʔ sā.mǔj]) is an island off the east coast of Thailand. Geographically in the Chumphon Archipelago, it is part of Surat Thani Province, though as of 2012, Ko Samui was granted municipal status and thus is now locally self-governing. Ko Samui, with an area of 228.7 square kilometres (88.3 sq mi), is Thailand's second largest island after Phuket. In 2018, it was visited by 2.7 million tourists.