I liked Jason Yip’s posting: No matter how many times you say it, we still don’t need a QA on the team – it really pins down the definition of the QA/QC terms.
In summary:
Quality Assurance (QA): The design and implementation of processes (roles + activities) to ensure quality in a system/product/service.
Quality Control (QC): The design and implementation of processes (roles + activities) to verify the quality of a system/product/service.
QA = prevent defects; QC = detect defects.