A French dip sandwich, also known as a beef dip, is a hot sandwich consisting of thinly sliced roast beef (or, sometimes, other meats) on a "French roll" or baguette.
It is usually served plain but a popular variation is to top with provolone cheese, onions, and a dipping container of beef broth produced from the cooking process (termed au jus, "with juice"). Beef stock, a light beef gravy, or beef consommé is sometimes substituted. The sandwich is most commonly served with a cup on the side of the plate, into which the sandwich is dipped as it is eaten, although this is not how the sandwich was served when it was originally developed. (Full article...)