The egg yolk is the yellow part of an egg, found at the center and surrounded by the egg white. It serves as a nutrient-rich source for the developing embryo in fertilized eggs. The yolk contains proteins, fats, vitamins, and minerals, making it a valuable food source for both humans and animals. In culinary uses, the egg yolk is often used in recipes for sauces, custards, and baked goods due to its ability to add richness and color. It is also a key ingredient in dishes like hollandaise sauce and mayonnaise, where it helps to emulsify and bind other ingredients together.