Quality assurance, or QA for short, is the systematic monitoring and evaluation of the various aspects of a project, service or facility to maximize the probability that minimum standards of quality are being attained by the production process. QA cannot absolutely guarantee the production of quality products. Note: if you mean measuring of system defectiveness, use "quality-assessment" tag
Two principles included in QA are:
- Fit for purpose - the product should be suitable for the intended purpose;
- Right first time - mistakes should be eliminated.
QA includes regulation of the quality of raw materials, assemblies, products and components, services related to production, and management, production and inspection processes.
Quality is determined by the product users, clients or customers, not by society in general. It is not the same as 'expensive' or 'high quality'. Low priced products can be considered as having high quality if the product users determine them as such.
Note: if you mean the process of evaluation of the software products quality, measuring of system defectiveness, use quality-assessment tag