The yolk is the yellow part in the center of an egg. When you crack open a chicken egg, you'll see the thick, golden yolk sitting in the middle of the clear, jelly-like egg white. The yolk contains proteins, fats, and nutrients that would feed a developing baby chick if the egg were fertilized.

In cooking, yolks are prized for their rich flavor and thick texture. They make sauces creamy, help bind ingredients together in baking, and give pasta dough its golden color. When you make scrambled eggs, you're mixing the yolk and white together, but some recipes call for separating them. A sunny-side-up egg keeps the yolk whole and runny in the center, perfect for dipping toast.

Birds, reptiles, and even some fish have yolks in their eggs, though chicken eggs are what most people think of. When someone talks about egg yolk in a recipe, they mean just the yellow center part, not the white.