In quality management, a nonconformity (also known as a defect) is a deviation from a specification, a "Norm (technology)" standard, or an expectation. It can be classified in multiple ways, although a typical classification scheme may have three to four levels, including critical, major, important, and minor defects.[1][2][3][4]​.

While some situations allow "nonconforming" and "defective" to be used synonymously, some industries distinguish between the two; Nonconformity represents a failure to meet an intended state and specification, while a defect represents a failure to meet normal usage requirements. requirement. A similar distinction is made between validation and verification.

When ensuring the quality of a product or service, the classification of non-conformities (non-conformities) is important, as it provides an opportunity to better reduce them.[1]​.

NASA recognizes the following types of nonconformity:[6][7]​.

Minor Nonconformity (NCm) - Any nonconformity that does not adversely affect airworthiness, performance, durability, interchangeability, reliability, maintainability, effective use or operation, weight or appearance (where this is a factor), health or safety. Multiple minor nonconformities when considered collectively can elevate the category to a major or critical nonconformity.

Major Nonconformity (NCM) - Any non-critical nonconformity that may result in failure or materially reduce the usability of the product for its intended purpose (i.e., effective use or operation, weight or appearance (where this is a factor), health or safety) and that cannot be completely eliminated by remanufacturing or reduced to a minor nonconformity by approved repair.

Critical nonconformity -Any nonconformity that may result in dangerous or unsafe conditions for people who use, maintain or depend on the product or impede the performance of a vital mission of the organization.

The ENAC, for its part, only recognizes the first two types of non-conformity[8]​.