A defect is a physical, functional, or aesthetic attribute of a product or service that exhibits that the product or service failed to meet one of the desired specifications. In simpler terms it can also be described as an output of a process that does not meet specification. Six Sigma aims to eliminate this completely or at least reduce the amount of defective outputs and variation to a certain acceptable level through the the different methodologies it applies.
Product defects arise most prominently in legal contexts regarding product safety, where the term is applied to “anything that renders the product not reasonably safe”
Finding the Cause
A wide range of circumstances can render a product defective. The product may have a design flaw, 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, or appropriate warnings of dangers accompanying normal use or misuse of the product.