Prevention. This comprises the costs of measures to prevent defects from taking place, such as training and process capability studies.
Appraisal. This comprises the costs incurred in detecting defects, which would include testing and inspection.
Internal and external failure. Internal costs are scrap, rework and the associated costs of not getting it right the first time. External failure costs are rectification after products have reached the final customer, such as warranty claims, returns and repairs.