A product defect is any characteristic of a product which hinders its usability for the purpose for which it was designed and manufactured. Product defects arise most prominently in legal contexts, where the term is applied to “anything that renders the product not reasonably safe for its intended use. This field of law that addresses injuries and death caused by defective products is called products liability.
A wide range of circumstances can render a product defective. The product may have a design defect, resulting from the product having been poorly designed or tested, so that the design itself yields a product that can not perform its desired function. Even if the design is correct, the product may have a manufacturing defect if it was incorrectly manufactured, for example if the wrong materials are used. A product may also be considered legally defective if it lacks appropriate instructions for its use.