1.quality: quality means, meeting requirements.fit for use.(质量就是满足需求，适合使用)
2.prevention:means to prevent quality defects or deficencies in the first place,and to make the products and processes assessable by quality management program.
（预防措施意味着防止质量缺陷或第一次的不足，通过质量管理程序使产品和过程可以顺利通过评估。） Prevention decreases production costs because the sooner a defect is located and corrected,the less costly it will be in the long run .The greatest payback is with prevention.
3.verification(验证)： the overall goal of verification is to ensure that each software product developed throughout the software life cycle meets the customer's needs and objectives as specified in the software requirements document.(验证的总体目标是确保每个软件产品开发的整个生命周期满足客户的需要和软件需求文档中描述的目标）
4.Validation checks that the system meets the customer's requirements at the end of the life cycle.(确认则是在生命周期结束时检查系统是否满足客户需求)
Usually verifications take place at the end of each phase.validations take place just before the product is delivered.
5.cost of quality: includes all costs incurred in the pursuit of quality or in performing quality-related activities.(prevention cost,（预防成本）Appraisal cost(鉴定费用)，internal failure cost ,external failure cost)(内部故障成本，外部故障成本)
prevention cost:quality planning,formal technical reviews, test equipment, training...
Appraisal costs: Inspection and testing of products,Equipment calibration (校准) andmaintenance- Processing and reporting inspection data
Internal failure costs :rework- repair- failure mode analysis
External failure costs ：- complaint resolution- product return and replacement- help line support- warranty work- future business losses