The primary ingredient in a meringue is egg whites. When whipped, egg whites can become airy and form stiff peaks, creating a light and fluffy texture. This reaction occurs due to protein denaturation, where proteins in the egg whites unfold and trap air, resulting in a stable foam. Sugar is then gradually added to the whipped egg whites to stabilize the structure and create a sweet flavor. Meringue can be further categorized into types such as French, Swiss, and Italian, depending on the method of preparation. It is commonly used in desserts like pavlova, macarons, and meringue pies.