ˈaɪsɪŋ ; ˈaɪsɪŋ(especially British English) (North American English usually frosting) [uncountable]
a sweet mixture of sugar and water, milk, butter or egg white that is used to cover and decorate cakessee also royal icing
the icing on the cake; (US also)
the frosting on the cake
something extra and not essential that is added to an already good situation or experience and that makes it even betterIt's an added bonus—the icing on the cake.