These terms are a source of confusion for Project Management test takers because they sound similar, and at a networking party, they might be used interchangeably. But per the PMBOK Guide, the difference between quality assurance and quality control is as follows:

• Quality assurance is about the project manager doing due diligence to make sure the processes and procedures are being followed correctly, as specified in the quality management plan.
• Quality control is the measurement and analysis of the test results on your deliverables to make sure the planned quality metrics are being met.