The term TKO Caller is a job title for a referee, which is a person responsible for enforcing the rules of a sport or game. The three-letter acronym 'REF' is used to refer to this position. A referee is responsible for making sure that all players abide by the rules and regulations of the game, as well as ensuring that the game is conducted in a fair and safe manner. They also have the authority to make decisions on any disputes that may arise during the game.