Stocks are flavorful liquids made by simmering bones, meat, seafood or vegetables in water. They are used as bases for soups, stews and sauces. The document discusses different types of stocks - white stocks made from poultry or veal bones, brown stocks made by first browning bones, and fish and vegetable stocks. It also explains techniques like court bouillon used for poaching fish, and remouillage which makes a weaker stock from already used bones. Key aromatic vegetables and flavorings used in stocks are also defined, such as mirepoix and bouquet garnie. Tips are provided for making high quality stocks through gentle simmering and removing impurities.