Quality Assurance is the process of reviewing a piece of work to ensure that the quality and standards are met.
Within software development, Quality Assurance is seen at various stages: during development, in testing, and upon acceptance. In development, Quality Assurance ensures the code that is being developed is up to the standards and is implemented in the correct method and format. In testing, Quality Assurance ensures that the code that is being developed is tested to perform as it should delivering the correct outputs. In client acceptance, it is the client ensuring that the quality of the final product that they are handed is meeting their standards and it is as they expected it to be.
