A stock is a liquid that can add flavor to ingredients. It is made by using simmered bones and helps brown it. Adding mirepoix or any other aromatics can make it have flavor.
White Stock- this stock is a soup stock made from veal or chicken without any colored seasonings and is used for white sauces. This stock is clear and pale that is made by simmering poultry, beef, or fish bones.
Brown Stock- this is a brownish liquid made by simmering poultry, beef, veal or bones that were browned first. This stock is usually made for gravy.
Fumet Stock- this is a highly flavored stock made by fish bones which has similarities to a fish stock. Its mostly made out of chopped fish heads and mirepoix.
Court Bouillon- this is an aromatic vegetable broth used for poaching fish or vegetables. It is usually used for poaching vegetables and meat for traditional uses.
Bouillon/Broth- also referred as broth, this stock has results from simmering meats or vegetables. It's a soup that is being prepare from broth or boil.
Jus- used as a sauce for roasted meat, this has a rich and slightly reduced stock
Vegetable Stock- used in soups with no meat, this is a vegetarian stock which is placed in water.
Glace Stock- a highly reduced stock that has a jelly like consistency and has high concentrated flavor. Once this stock is cool it becomes a rubber consistency.
Stocks are important in cooking because they could add flavor to many different food like meat and vegetables. It helps give the food a better taste and makes it delicious which is why it's been around for many years. A liquid that simmers the bones can make soup or ingredients become a better dish than it was before.