The umpire is the person charged with officiating the game, including beginning and ending the game, enforcing the rules of the game and the grounds, making judgement calls on plays, and handling the disciplinary actions. The term is often shortened to the colloquial form ump. They are also sometimes addressed as blue at lower levels due to the common colour of the uniform worn by umpires.
To learn more and start umpiring visit the Umpire WA website.