The term "hidden vegetables" refers to a cooking technique where vegetables are blended or pureed into a food product, such as a sauce, soup, or baked good. This method is used by chefs to add extra nutrients and flavor without altering the appearance of the dish. The term can also be used more broadly to refer to any ingredient that is added to a recipe but not immediately visible or noticeable in the final product, such as pureed tomatoes in spaghetti sauce or grated carrots in muffins.