Quality Assurance is about Process.  It describes the proactive method of establishing a process that is capable of producing a product or deliverable that is error or defect free.   Expanding on this further, we can see that:

1. Quality Assurance means time is spent upfront planning and designing a process that can repeatedly produce a high quality product or deliverable.
2. Quality Assurance provides confidence that if the process is properly followed, there is a high likelihood that the final product or deliverable will meet specifications.  In other words, it reduces and prevents defects or errors in the final product or deliverable.
3. Quality Assurance is about establishing a sound and capable process.

Quality Control is about Products or Deliverables.  It describes checking a final product or deliverable to ensure that it is defect or error free and meets specifications. 

1. Quality Control occurs after the process is completed.
2. Quality Control is about verifying that the product or deliverable meets specifications. It detects errors and defects in the final product before the product reaches the customer.
3. Quality Control focuses on the end product or deliverable.

To summarize, Quality Assurance is focused on the process, is proactive, and prevents defects; while Quality Control is focused on the product or deliverable, is reactive, and detects defects after the fact.