After a food has been sauteed or roasted, it is removed from the pan - and the excess fat is spooned out.
What remains are the fonds, or caramelized bits of juice, from the natural sugars in the meat or vegetables that have been cooked. They stick to the pan and form a glaze.
These intensely flavorful, browned bits are deglazed by heating a bit of liquid--usually stock or wine--in the pan. The bits are scraped up to form a mixture that can be used as a sauce for the cooked food.

Instructor: Paul Grimes