A product may have many defects – imperfections. But a product is not defective unless the defects prevent the product from functioning. If a product is not usable, it is considered defective.
Defects may be many on a shippable and acceptable product. An example is typos in a book. A typo is a defect, but the book ships to satisfied customers. A defective book would probably fall apart.
Ex. An undercooked hamburger cannot be used (consumed) by the customer. Other items (unevenly browned fries, underweight hamburger, too much ice in a drink) have flaws or defects, but you can still sell them and customers can still consume them. They do not need to be scrapped, so they are not truly defective.