A sundae is an ice cream dessert. A sundae is made of finished soft ice cream with jam and nuts, so the raw material of a sundae is mainly ice cream powder or ice cream milk. Traditional sundaes will use one or two spoonfuls of ice cream with jam or syrup on it, and some also use a layer of icing, whipped cream, cherries or other fruits (bananas, pineapples) on it.
McDonald's ice cream "Xindi" is the same as KFC's "sundae", and the English name is sunday, which means Sunday. The two companies have different names because of different transliteration.