Au jus is French for "with [its own] juice"; jus is the juice itself. 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. In French cuisine, jus is a natural way to enhance the flavour of dishes, mainly chicken, veal and lamb.
Ingredients and preparation 
'Jus' means the natural juices given off by the food. To prepare a natural jus, the cook may simply skim off the fat from the juices left after cooking and bring the remaining meat stock and water to a boil. Jus can be frozen for six months or longer, but the flavor may suffer after this time.
American recipes au jus often use soy sauce, Worcestershire sauce, salt, pepper, white or brown sugar, garlic, onion, or other ingredients to make something more like a gravy. So-called jus is sometimes prepared separately, rather than being produced naturally by the food being cooked. An example could be a beef jus made by reducing beef stock to a concentrated form, (also known as Glace de Viande) to accompany a meat dish.
Jus can also be made by extracting the juice from the original meat and combining it with another liquid e.g.: red wine (thus forming a red wine jus).
A powdered product described as jus is also sold, and is rubbed into the meat before cooking or added afterwards. Powdered forms generally use a combination of salt, dried onion, and sometimes sugar as primary flavoring agents.
English language 
In an entrenched United States usage, the term "au jus" has become corrupted from the French meaning and pronunciation; it is commonly used to refer to the broth, rather than its literal translation, "with the broth", and the silent s is pronounced. So rather than a "sandwich au jus", the menu may read "sandwich with au jus". It is typically served with the French dip sandwich.
- "Justin Quek: Passion & Inspiration", Justin Quek with Tan Su-Lyn, Bon Vivant Publishing Pte Ltd, 2006, Page 30
- Labensky and Hause (1999), On Cooking, Prentice-Hall
- Garner, Bryan A. (2000). The Oxford Dictionary of American Usage and Style. Oxford University Press. p. 33. ISBN 978-0-19-513508-4. Retrieved 2013-01-06.