A French term, Demi-glace is a type of brown sauce common to the culinary industry. It is traditionally made by combining equal parts of beef or veal stock and espagnole which is then simmered and reduced by half. The result is a thick, rich sauce well suited for meats and other rich dishes.
It has a strong taste and is rarely used directly on food.
As a mother sauce, however, it then serves as the starting point for many derivative sauces, such as: Sauce Africaine, Sauce Bigarade, Sauce Bourguignonne, Sauce aux Champignons, Sauce Charcutiere, Sauce Chasseur, and Sauce Chevreuil, just to go as far as the "Cs". There are hundreds of other derivatives in the classic French repertoire.