Wiktionary
n. (alternative spelling of demiglace English)
Wikipedia
Demi-glace (English: "half glaze") is a rich brown sauce in French cuisine used by itself or as a base for other sauces. The term comes from the French word glace, which, used in reference to a sauce, means icing or glaze. It is traditionally made by combining equal parts of veal stock and espagnole sauce, the latter being one of the five mother sauces of classical French cuisine, and the mixture is then simmered and reduced by half.
Common variants of demi-glace use a 1:1 mixture of beef or chicken stock to sauce espagnole; these are referred to as "beef demi-glace" (demi-glace au boeuf) or "chicken demi-glace" (demi-glace au poulet). The term "demi-glace" by itself implies that it is made with the traditional veal stock.
Usage examples of "demi-glace".
There are a lot of ways to make demi-glace, but I recommend you simply take your already reduced meat stock, add some red wine, toss in some shallots and fresh thyme and a bay leaf and peppercorns, and slowly, slowly simmer it and reduce it again until it coats a spoon.
To me, life without veal stock, pork fat, sausage, organ meat, demi-glace, or even stinky cheese is a life not worth living.