Stock is a thin liquid made by boiling bones, meat scraps, and vegetables to extract flavor. There are several types of stock - white stock made from veal, brown stock made from beef bones, chicken stock with a pale yellow color, and fish stock with rich fish flavor. Proper preparation of stock involves using cold water, slow simmering, skimming scum regularly, quick cooling, and refrigeration. Stocks provide flavor foundations for soups and sauces and can be stored in the refrigerator for 2-3 days or freezer for 7-10 days.