Two terms that have many interpretations because of the multiple definitions for the words assurance and control. One definition of quality assurance is: all the planned and systematic activities implemented within the quality system that can be demonstrated to provide confidence that a product or service will fulfill requirements for quality. One definition for quality control is: the operational techniques and activities used to fulfill requirements for quality. Often, however, “quality assurance” and “quality control” are used interchangeably, referring to the actions performed to ensure the quality of a product, service or process.

http://asq.org/learn-about-quality/quality-assurance-quality-control/overview/overview.html