Some people use these terms interchangeably but there is a technical difference. Frosting usually begins with butter which is why it's known as buttercream since it's rich in butter and creamy. Frosting is typically fluffy and thick. Icing is thinner than frosting but thicker than a glaze, and is usually made by combining powdered sugar (also called icing sugar in some places!) with some type of liquid. Icing can be drizzled or spread and is smoother and shinier than frosting. These peach cupcakes have frosting since it's thick, buttery and rich!