The term MCFLY in the movie 'Back to the Future' refers to Marty McFly, the protagonist of the film. Marty is a teenager from Hill Valley, California who is sent back in time to 1955 by his friend Dr. Emmett Brown. He must find a way to get back to the future and save his family from an uncertain fate. Marty's adventures in the past and his attempts to return to the future form the basis of the movie's plot.