Functionary is a term often used to describe a person who plays a role in a Toastmasters meeting or contest. Toastmasters International seems to prefer the use of the term "participant role" or meeting role  instead. Some clubs use the term "assistant" for some of the roles. Typical functionary roles may include Ah Counter, Balloter, Sergeant-at-Arms and others.
A functionary should not be confused with a dignitary.