Gravy
Gravy is a thickened sauce, usually made based on the juices and extractives which run out from meat during cooking. Today, completely vegetable-based gravies are also made.There are two basic types of meat gravy: thickened and unthickened. The unthickened gravy, in the case of red meats, is often referred to as "au jus". This is simply a cooked mixture of blood and tissue juices.
Thickened gravies are usually made starting with a roux. This is a mixture of fat and flour. The other liquids are added gradually, while continually stirring the mixture, to ensure that it mixes properly.
Many gravies contain milk or cream as well as meat or vegetable juices. Sometimes finely-cut meat bits are added back into the gravy.
Some cooks routinely season gravy more than would be desirable for eating it as a dish by itself, because it is almost always used as a sauce over other foods that are often blander.
A favorite American dish is mashed potatoes and gravy; this is the most common use for gravy. Gravy is also commonly poured over meat, biscuits, and stuffing.
see also the Wikipedia Cookbook