There are three general types of product defects:

Design failure — When there is a critical error at the design stage of a product's development, every single one of those products will be dangerous. A good example of a design flaw is the infamous exploding gas tank on the Ford Pinto.

Manufacturing failure — Sometimes products are designed safely, but an individual production run may have had some error that makes the product unsafe.

Failure to warn — When a manufacturer can anticipate that someone may use a product for an unintended, but foreseeable, use that could be hazardous, the manufacturer needs to warn of the risk of that type of use.