Someone who works in concessions-- typically at a movie theatre. Its technically not a word according to most dictionaries, and usually gets the red squiggly line from most spell-checkers; but you can refer to this unofficial definition as your own little victory knowing that, as far as the rest of the world is concerned, its a real word.
* These videos are coming directly from Youtube, they may or may not be most relevant to the word "Concessionist"
What is Define Dictionary Meaning?
Best thing is, its free and you can even contribute without creating an account.