Royal icing is a type of icing made from egg whites and powdered sugar. It is known for its smooth, glossy finish and is often used to decorate cookies and cakes. The icing hardens when it dries, making it ideal for intricate designs and detailed decorations. This icing can be piped into various shapes and is commonly used in sugar cookies for events like Christmas and weddings. Additionally, it can be colored with food coloring to create vibrant designs. Royal icing is also popular for creating gingerbread houses due to its strong adhesive properties.