QoS
QoS was defined in the ITU standard X.902 as "A set of quality requirements on the collective behaviour of one or more objects."
In computer networking, the traffic engineering term Quality of Service refers to resource reservation control mechanisms. Quality of Service provides different priority to different users or data flows, or guarantees a certain level of performance to a data flow in accordance with requests from the application programme or user policy. A practical example of this is where a voice call is being made through VoIP, QoS will dictate that voice calls will always have priority over 'normal' data traffic.