A stock is a flavorful liquid that is made by simmering bones and\or vegetables. The stock is often called the chef's "building blocks" Stocks can be soups or sauces. By adding mirepoix or aromatics the stock can be given flavor.
White stock: Clear pale liquid made by simmering poultry,beef, or fish bones.
Brown Stock: Another liquid made by simmering poultry,beef,veal, or game bones that have been browned first.
Fumet: Similar to fish stock, this is a highly flavored stock made with fish bones.
Court Bouillon: Aromatic vegetable broth used for poaching fish or vegetables
Glace: Occasionally referred to "glaze," this is a reduced stock with a jelly-like consistency, made from brown stock, chicken stock, or fish stock.
Remouillage: A weak stock made from bones that have already been used in another preparation, sometimes uses to replace the water as a liquid used in a stock; it is the french word for "rewetting."
Bouillon: liquid that results from simmering meats or vegetables; also referred to as broth
Jus: Rich, lightly reduced stock used as a sauce for roasted meats.
Vegetable stock: Made from mirepoix,leeks, and turnips. When adding the tomatoes,garlic and seasoning the tomato must be strained with cheesecloth or filter. A chef might roast the vegetables or add a large amount of a vegetable like mushrooms for a mushroom stock.
Stocks are very important to the culinary arts because if you master the stocks it will help guide you into creating deep rich flavors in other food. Also, because stocks will help with making the sauces and understanding each one.