Meringue is a light, sweet foam made by whipping egg whites and sugar together until they form stiff, glossy peaks. When you beat air into egg whites vigorously (usually with an electric mixer), they transform from clear, runny liquid into a white, fluffy cloud that can hold its shape. Adding sugar while beating makes the foam stable and sweet.

Bakers use meringue in many ways. They pipe it onto pies (like lemon meringue pie) and toast it with a kitchen torch until the peaks turn golden brown. They bake meringue cookies that are crispy on the outside and melt on your tongue. Meringue can also be folded into other ingredients to make them lighter and airier, like in a soufflé or certain cake batters.

The key to good meringue is patience: you need to beat the egg whites long enough, and even a tiny bit of egg yolk can prevent the whites from forming those crucial stiff peaks. When done right, meringue is one of baking's little miracles, turning simple ingredients into something that seems almost impossibly light.