Wiktionary
Etymology 1 a. (of a sandwich) prepared or served with the jus from roasted meat Etymology 2
n. the jus itself, when something is served ''au jus''
WordNet
adj. served in its natural juices or gravy; "roast beef au jus"
Wikipedia
Au jus is a French culinary term meaning "with juice". It refers to meat dishes prepared or served together with a light gravy made from the juices given off by the meat as it is cooked. In French cuisine, cooking au jus is a natural way to enhance the flavour of dishes, mainly chicken, veal, and lamb. In American cuisine, the term is mostly used to refer to a light sauce for beef recipes, which may be served with the food or placed on the side for dipping.
Usage examples of "au jus".
AFTER LUNCHEON -the traditional shrimp cocktail, 'native' snapper with a minute paper cup of tartare sauce, roast prime ribs of beef au jus, and pineapple surprise- it was time for the siesta before meeting Goldfinger at three o'clock for the afternoon session.
The meals for this flight are Chicken Kiev with rice, Roast Beef au Jus with baked potato, and for the weight-watchers among us, Orange Ruffy and stir-fried veggies - and if you believe that, sir, you've been staring at the instrument panel too long.
There were places where they specialized in thick red roast beef au jus, or roast chicken basted in wine.