Quality Control and Quality Assurance
Quality Assurance deals with 'prevention' of defects in the product being developed. It is associated with the process and process improvement activities. Testing means "quality control". Its focus is defect detection and removal. Quality Control measures the quality of a product. Quality Assurance measures the quality of processes used to create a quality product. [Software Testing and Quality Assurance published by Nirali Prakashan]
Quality Assurance is a set of activities designed to make sure that the development and/or maintenance process is adequate to ensure a system will meet its goals. Quality assurance is an activity that establishes and assesses the processes that produce products. If there is no need for process, there is no role for quality assurance. Quality assurance is a management responsibility, frequently performed by a staff function.
Quality Control is a set of actions or activities designed to evaluate a developed work product. Quality control activities focus on identifying defects in the actual products produced.
Also See:
Difference between Software Testing & Quality Assurance