QA and QC 

What's the difference between Quality Assurance and Quality Control? Is there one?

It's not at all uncommon to hear someone talk about 'QA' when what they actually mean is 'QC'. Or vice versa.  Or even perhaps, quality management. Although one must admit that 'QA' rolls off the tongue far more easily than QC and a whole lot more easily than 'QM'.

QA and QC are closely related. They are both part of quality management.  But they are different .

What QC is

The C in QC gives you the clue: it's about controlling quality.  QC is about inspections, checks and tests.  

QC is used to distinguish between what's 'good' (OK, passes, meets requirements, conforms, whatever you want to call it) and what's 'bad' (not OK, fails the test, doesn't conform, nonconformity, nonconforming product or service, doesn't meet requirements).

The focus of QC is to verify the quality of the output: of the service or product delivered to a customer, but often also involves tests, checks, measurements or other activities on parts or components or important stages before the service/product reaches 'final' status. 

Examples of QC for servicesQA_QC

Examples of QC on product

What QA is

The A in QA stands for Assurance.  It's about assuring quality (yes, really). 

QA involves thinking about what is required to ensure quality will be achieved, and to set out processes, standards, procedures and/or policies to do that.  Typical results of QA are quality plans, inspection and test plans (ITPs), documentation and training.  It moves a step up from finding the failures to aiming to prevent or eliminate them.

The focus of QA is to provide confidence that requirements and standards are met, and that processes and system have been followed.  

Examples of QA

What ISO 9000 says

Since this site is focussed on ISO 9001, a brief look at what ISO 9000 has to say.

Quality control is defined as: “A part of quality management focused on fulfilling quality requirements”  (clause 3.2.10, ISO 9000) 

Quality assurance is defined as that “part of quality management focused on providing confidence that quality requirements will be fulfilled” (op cit, clause 3.2.11)

Quality management: 'coordinated activities to direct and control and organization with regard to quality' (op cit, clause 3.2.8.

Hmm.  As I've said elsewhere, ISO 9000 makes for very dry reading. These definitions give you a clue as to why, and are really rather broad and not terribly useful.

Why you need QA and QC 

If the only part of quality you use is QC, you would be constantly checking, measuring and testing your services or widgets, but even when you found some that failed, you wouldn't ever do anything to your system to improve it, to understand and eradicate problems you find when inspecting, testing or measuring or attempt to remove those failures.  

If you only used QA, you would perhaps have what look like/sound like a great set of processes and paper work.  But you never actually test, check or measure the product or service to verify that it actually does what it is supposed to do.  (Which doesn't say a lot for assurance, in my eyes.) 
In either case, the service or product is unlikely to meet what your customer wanted and expected. 

Quality management

And then there's quality management, which includes QC and QA as well as a bunch more things.