The yolk is the yellow, nutrient-rich part of an egg, found at the center. It serves as the primary source of food for the developing embryo in birds and reptiles. The yolk contains proteins, fats, vitamins, and minerals, making it an essential component of the egg. In cooking, the yolk is often used in various recipes, such as sauces, custards, and baked goods. It contributes to the flavor, color, and texture of dishes. The yolk can be separated from the egg white for specific culinary purposes, allowing for a range of cooking techniques and presentations.