[#qa]: QA / Q&A
QA: Quality Assurance

Effectively the same thing as QC: Quality Control. This term refers to efforts expended to make sure that any product/service experienced by an end user has high quality. Another similar term may be “End user experience”.

Q&A: Question-and-answer

A format where information is presented by listing questions and listing answers.

QC: Quality Control
[#qos]: “quality of service” (“QoS”)

Refers to prioritization, particularly when related to network traffic. Traffic which is considered to be high priority may actually be given high priority. Applications such as VoIP may often require low bandwidth, but may be highly sensitive to latency. This means that they use up fairly little data, but the data really needs to go quickly or else there is a high chance that people will become unhappy with the service.

Low bandwidth traffic which is less tolerant of latency, such as real-time voice applications, may be marked in a way so that they are given higher priority than bandwidth which is more tolerant of latency (and often higher bandwidth). (VoIP is a classic example commonly used when describing QoS.) This way, a telephone call's traffic doesn't need to wait for a large E-Mail to be sent. People are generally used to needing to wait for E-Mail, so delaying an E-Mail by a matter of seconds may not be surprising and may very often be unnoticed. However, if the voice data of a phone becomes unavailable for a short period of time, then people may notice problems such as voice cutting out. This may often be more noticeable by people, affecting the experience in a way that people will generally consider to be impacting and undesirable. In contrast, sending an E-Mail is often given a low priority, because people are less likely to notice or care much if E-Mail takes an extra four seconds.