Quality assurance ensures the customers and stakeholders have a sense of confidence that the quality requirements will be met and fulfilled. It goes beyond simply controlling processes.
The ISO definition of quality assurance is: "part of quality management focused on providing confidence that quality requirements will be fulfilled".
Quality assurance encompasses many wider factors to quality control, such as planning, design, improvement, and responsiveness to changing customer expectations.
This is a way of intercepting defects earlier on in the process, which is how it differs from quality control. These defects may be related to faults in products manufactured or problems when providing service to customers.