Quality Assurance is the component of quality management that focuses on assuring the fulfilment of quality requirements. There are two prongs to quality assurance:
1. an internal prong, to management, and
2. an external prong, to customers, certifiers, government agencies, and third parties.
Another way to define QA is to say it comprises all “planned and systematic activities” existing within the quality system that definitely provide confidence that a product or service delivers on promises of quality.
To summarize this, quality assurance aims to prevent defects by ensuring that the approaches, methods, processes, and techniques are specific to a project. That implementation is as correct as it's thorough.
The activities of quality assurance monitor and ensure adherence to the processes for managing and creating the deliverables. It also ascertains that these processes are operative.
By highlighting flaws in the process, Quality Assurance is proactive and preventive. Naturally, it precedes Quality Control.