(Quality of Service)
In traditional phone networks, QoS refers to a wide range of connection quality measurements. Connection delay and interference may be measured, as well as sound quality and volume, and echo.
In more modern digital data networks, QoS can refer to specific standards for prioritizing time-sensitive data, such as real-time audio and video connections, including VoIP and video calling.
Typical bits of data - such as a web page - can be delayed by fraction of a second with minimal impact for the end user. However with audio/video data (and real-time gaming data) even the shortest delay can have a large negative impact for the end user, making it impossible to have a voice conversation over a data network.
QoS attempts to address this with a variety of techniques designed to ensure that data for real-time applications is prioritized over less time-sensitive data, and delivered with minimal delay.