A grid official is someone who is responsible for officiating a game or match. The four most common grid officials are linesman, REF, UMP, and REFEREE. A linesman is an official who assists the REFEREE in making decisions during a game. A REF is a shortened version of the word REFEREE, which is the main official in charge of the game. An UMP is another term for an umpire, which is an official who makes sure the rules of the game are followed. Lastly, a REFEREE is the main official in charge of the game who is responsible for making sure the rules are followed and that the game is fair.